M
mauidan
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I agree, excellent read, and I would extend that to the whole series that Michael is doing and that he should conclude with some comparisons of various combinations of these devices.
I really disliked Mr. Moffat's insinuations as 'Manufacturer's Comments' - showed a good lack of class IMO. Not saying their product isn't good by the way.
Don't invoke the Devil
bzr
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FlexibleAudio
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Regardless of what Mike Moffat says in the comments section, he needs to understand that "Uptone are the only experts in this very specialist emerging area." I know this because Norman told me this in Post #71 of the "Regen Wow" thread. Norman would never spew hyperbola. Apparently its also true that DHT's are in fact flat from 20hz to 20khz, that usb is superior to I2S, that a balanced dac topology is vastly superior to an unbalanced topology (merely because dac chips are naturally balanced), and pigs can fly.
Here are some of Mike Moffat's Comments from the article regarding the Regen:
"I would like to thank Mr. Lavorgna for taking the time to review the Schiit Wyrd, with the link in the review to the Uptone Audio REGEN, a product with which I was not familiar. I have a policy of not commenting on the designs of others – this time, however, I feel a need to make objective comments, due in fact to the link to the other product within the Wyrd's review.
It is flattering when another manufacturer builds a nearly part by part copy of one of Schiit's current products, in this case a USB hub based, crystal clock driven, repeater type design with a power supply to drive the USB+5.
It is really helpful to me when products I have introduced (or re-introduced) are rebuilt by others with their own modifications added. This is simply because those who matter most always know who built it first."
—Mike Moffat, Co-Founder Schiit Audio
Someone is fibbing, but pigs can still fly. When I tried to point out to Norman the extreme nature of his claim and mentioned that others including Playback Designs, MSB and Berkeley (to name a few) have also done much in this this area I got the same circular run around I always get. The concerning thing to me is I see many Sharks taking his comments as fact. I have tried to address the situation but frankly its a full time job and I am tired.
Before you start screaming, the following is a note to my critics (from my post #67 in the "Regen Wow" thread)--
I am not here for flames. I am here to learn. I also, however, care a lot about the integrity of this forum. If we are so "friendly" we can never have in intelligent discourse to clarify or correct a members posts then the average quality of information available will suffer. I do not think this is a good thing. If comments do not need to meet a minimum standard because they can not be challenged I think our membership will gradually migrate to places where the average value is higher than we provide. Evaluating the reasoning behind disagreements is our de facto Quality Control Department and with out it our quality will suffer. I am NOT a proponent of allowing the kind of personal confrontation that occurs on other forums but the pendulum swinging to far the other way can undermine what imo is our primary purpose here.
Here are some of Mike Moffat's Comments from the article regarding the Regen:
"I would like to thank Mr. Lavorgna for taking the time to review the Schiit Wyrd, with the link in the review to the Uptone Audio REGEN, a product with which I was not familiar. I have a policy of not commenting on the designs of others – this time, however, I feel a need to make objective comments, due in fact to the link to the other product within the Wyrd's review.
It is flattering when another manufacturer builds a nearly part by part copy of one of Schiit's current products, in this case a USB hub based, crystal clock driven, repeater type design with a power supply to drive the USB+5.
It is really helpful to me when products I have introduced (or re-introduced) are rebuilt by others with their own modifications added. This is simply because those who matter most always know who built it first."
—Mike Moffat, Co-Founder Schiit Audio
Someone is fibbing, but pigs can still fly. When I tried to point out to Norman the extreme nature of his claim and mentioned that others including Playback Designs, MSB and Berkeley (to name a few) have also done much in this this area I got the same circular run around I always get. The concerning thing to me is I see many Sharks taking his comments as fact. I have tried to address the situation but frankly its a full time job and I am tired.
Before you start screaming, the following is a note to my critics (from my post #67 in the "Regen Wow" thread)--
I am not here for flames. I am here to learn. I also, however, care a lot about the integrity of this forum. If we are so "friendly" we can never have in intelligent discourse to clarify or correct a members posts then the average quality of information available will suffer. I do not think this is a good thing. If comments do not need to meet a minimum standard because they can not be challenged I think our membership will gradually migrate to places where the average value is higher than we provide. Evaluating the reasoning behind disagreements is our de facto Quality Control Department and with out it our quality will suffer. I am NOT a proponent of allowing the kind of personal confrontation that occurs on other forums but the pendulum swinging to far the other way can undermine what imo is our primary purpose here.
Mhhh
Very classy response. I know who my money is on as the truther vs the fibber:
image: http://cdn.audiostream.com/images/user_account_pictures/picture-30922-1394495689.jpg
Let's put a rest to this please... Submitted by UpTone Audio on August 13, 2015 - 11:20am
[Gentlemen: I composed the below in a word processor in-between other tasks this morning. Now going to post it I see that others have chimed in with regards to Schiit’s comments concerning the REGEN. While it is worth setting the record straight, “crapping up” the Wyrd’s review with further comments about this would be distasteful. So although I appreciate the support from REGEN fans, I am going to post the below and ask that this be the last word on the matter.
Thanks.]
Mike Moffat and Jason Stoddard are audio pioneers and engineers whom I have long respected, and I admire the straight-shooting, value-oriented company they have built. (As a serial audio entrepreneur myself, I laughed and cried through Jason’s entire blog/book, “Schitt Happened…”, because I so identified with many of their travails.) I fact, I have been considering picking up the intriguing Schiit Yggdrasil for my own system.
Thus I was somewhat saddened to see that Mr. Moffat used his Manufacturer’s Comment to accuse us of blatantly copying the Wyrd in our design of the UpTone USB REGEN. Such a charge would be of serious concern if true, but both public and private records show this is not the case at all.
My engineering partner, John Swenson, had been studying and writing about (see the series of Q&A interviews right here on AudioStream dated August 2013) issues of USB signal integrity for some time, and the first prototypes of our REGEN pre-date Schiit’s March 2014 announcement of Wyrd (and what appears to be June 2014 first shipments) by several months. Believe me, I felt a big lump in my stomach when I read about the hub-chip-Wyrd as we were readying first production of the REGEN.
So while it is true that both the REGEN and Wyrd use the same model of USB2.0 hub chip, that’s an easy coincidence because of our common desire to pick an older device with less “crap” going on it, and for that there just are not very many. I think the similarities between our product designs and their goals pretty much end there. The REGEN focuses on optimized signal integrity and ideal impedance match—best when positioned right at the DAC’s input jack—while the Wyrd appears to concentrate most of its circuitry on providing very clean 5VBUS for DACs that need it. Their own marketing seems to indicate that inclusion of the hub chip is to help in instances where computer/DAC combos “make weird noises or have glitches.”
Again, with much respect to Mike Moffat and his team, I can promise that UpTone Audio products never have and never will copy other’s work (life is too short and I’m too old for unoriginality). The REGEN/Wyrd overlap is simply a case of great minds thinking alike.
Sincerely,
Alex Crespi
UpTone Audio LLC
Read more at Schiit Wyrd USB Power Isolator | AudioStream
Very classy response. I know who my money is on as the truther vs the fibber:
image: http://cdn.audiostream.com/images/user_account_pictures/picture-30922-1394495689.jpg
Let's put a rest to this please... Submitted by UpTone Audio on August 13, 2015 - 11:20am
[Gentlemen: I composed the below in a word processor in-between other tasks this morning. Now going to post it I see that others have chimed in with regards to Schiit’s comments concerning the REGEN. While it is worth setting the record straight, “crapping up” the Wyrd’s review with further comments about this would be distasteful. So although I appreciate the support from REGEN fans, I am going to post the below and ask that this be the last word on the matter.
Thanks.]
Mike Moffat and Jason Stoddard are audio pioneers and engineers whom I have long respected, and I admire the straight-shooting, value-oriented company they have built. (As a serial audio entrepreneur myself, I laughed and cried through Jason’s entire blog/book, “Schitt Happened…”, because I so identified with many of their travails.) I fact, I have been considering picking up the intriguing Schiit Yggdrasil for my own system.
Thus I was somewhat saddened to see that Mr. Moffat used his Manufacturer’s Comment to accuse us of blatantly copying the Wyrd in our design of the UpTone USB REGEN. Such a charge would be of serious concern if true, but both public and private records show this is not the case at all.
My engineering partner, John Swenson, had been studying and writing about (see the series of Q&A interviews right here on AudioStream dated August 2013) issues of USB signal integrity for some time, and the first prototypes of our REGEN pre-date Schiit’s March 2014 announcement of Wyrd (and what appears to be June 2014 first shipments) by several months. Believe me, I felt a big lump in my stomach when I read about the hub-chip-Wyrd as we were readying first production of the REGEN.
So while it is true that both the REGEN and Wyrd use the same model of USB2.0 hub chip, that’s an easy coincidence because of our common desire to pick an older device with less “crap” going on it, and for that there just are not very many. I think the similarities between our product designs and their goals pretty much end there. The REGEN focuses on optimized signal integrity and ideal impedance match—best when positioned right at the DAC’s input jack—while the Wyrd appears to concentrate most of its circuitry on providing very clean 5VBUS for DACs that need it. Their own marketing seems to indicate that inclusion of the hub chip is to help in instances where computer/DAC combos “make weird noises or have glitches.”
Again, with much respect to Mike Moffat and his team, I can promise that UpTone Audio products never have and never will copy other’s work (life is too short and I’m too old for unoriginality). The REGEN/Wyrd overlap is simply a case of great minds thinking alike.
Sincerely,
Alex Crespi
UpTone Audio LLC
Read more at Schiit Wyrd USB Power Isolator | AudioStream
Wow, what interesting talk about i2s and Signal integrity. Let's see this dates back to...Aug, 2013!
that cant be right now, can it?
[h=2]Q&A with John Swenson. Part 2: Are Bits Just Bits?[/h]
By Michael Lavorgna • Posted: Aug 28, 2013
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image: http://cdn.audiostream.com/images/styles/600_wide/public/82813js2_0.jpg?itok=ks7UQbMD
In Part 1 of our Q&A, John Swenson covered "What is Digital?". You should consider that required reading for Part 2 since he builds on that foundation here. Part 1 also includes John's bio if you'd like to know more about him. Now let's get on with Part 2:
Can you explain how things other than "the bits" could have an effect on the analog output of a DAC?
First I’m going to go into some more detail on what I talked about last time, specifically, ramp times. Remember that the jitter caused by the ramp time is a combination of the threshold uncertainty and the ramp time. So it seems at first glance that you can decrease the jitter by having a faster ramp time. Unfortunately it doesn’t work that way.
The same amount of charge needs to be transferred no matter what the ramp time is. So if it takes one half the time, twice as much current has to flow. This causes the ground plane noise to increase, which increases the threshold uncertainty. Thus decreasing the ramp time doesn’t help.
"The result is that faster ramp times actually increase jitter."
It’s actually worse. If you run the “edge” through a Fourier transform (which converts the time domain into a frequency domain) you will see a large amount of very high frequency components. If you decrease the ramp time, those high frequency components increase. When those high frequency currents flow through the inductance in the ground plane they create an even greater voltage drop than already mentioned. The result is that faster ramp times actually increase jitter.
I covered this in detail to show how what seems obvious at first glance may not actually be true when you start dealing with jitter and ground plane noise.
So what about an asynchronous USB interface, isn’t it supposed to completely isolate the DAC from everything? Let’s look in detail at each part of the system and see what affects it.
Let’s start with the local oscillator, the “clock”. It turns out that almost all ultra low jitter oscillators are quite sensitive to ground plane and power supply noise. As the noise increases the jitter increases, and the spectrum of that extra jitter is directly related to the spectrum of the noise. This phenomenon is well known by many digital designers, so many will use decent low noise regulators with the clocks, but many don’t bother with that step, guaranteeing that the low jitter spec of the oscillator is going to be drastically compromised. Not only do you have to deal with the self generated noise of the regulator, but also its ability to block noise coming in on its input supply. Most regulators are very poor at this for high frequencies. This means that noise generated by the other logic elements on the board is going to sail right on through the regulators used in many DACs, causing jitter in the clock whose spectrum is highly correlated to what the rest of the board is doing. It IS possible to do a good job of providing low noise clean power to the clock, but it’s not easy and the designer really has to work at it.
And we still haven’t even talked about the ground plane! The noise on the ground plane is just as important to the jitter of the clock, but it doesn’t have a regulator, it just is what it is. If the clock is going to do what it is supposed to do, the ground plane it is connected to HAS to somehow be isolated from the noise generated by other parts of the circuit. I’ll go into this in detail later on.
So right at the beginning the clock itself is susceptible to influences outside itself in almost all implementations.
After the clocks (it takes two in most implementations) you need a clock mux, which again creates its own jitter from the ground plane noise caused by the return current going back to the clock. In order to decrease this jitter you need to make the ramp time of the clock slow, but not too slow. The adage here is “just fast enough to work in all circumstances”. That means you usually have to slow down the clock edges. Fortunately this is easy to do by just putting a resistor in series with the output. But just this simple little tweak is not done very often. And what about the mux itself? It needs to have the same treatment. Fortunately the designer has a large choice of possible muxes to choose from, some very fast edges and some very slow. As strange as it may seem frequently the best ones to use are the old slow technologies from decades ago. They lumber along with slow edge rates and internal transistors, creating very small amounts of noise. Since the clocks we are talking about here are very slow by modern standards, these old muxes work very well. But again, not many designers take the time to optimize that.
"Most modern DAC chips have a lot of stuff inside creating a lot of noise on the internal power and ground traces, which pretty much nullifies that ultra low jitter clock we are sending it."
Then the clock goes to the DAC chip. Most modern DAC chips have a lot of stuff inside creating a lot of noise on the internal power and ground traces, which pretty much nullifies that ultra low jitter clock we are sending it. This is probably why a large number of people have a hard time hearing differences caused by changes to things such as jitter and noise. The effects caused by them are being swamped by the jitter generated inside the chip.
A number of companies are realizing this and are using DAC chips where a lot of this internal processing can be turned off. This significantly cuts down on internal jitter, BUT it also makes it possible for external influences to be more noticeable. So now the jitter on the main clock fed into the DAC chip starts to be quite important since it’s not masked so much. An analogy might be the noise level in your listening room. Let’s say you have a fan running and you realize that it’s interfering with your enjoyment of the music. So you turn the fan off, expecting perfect quiet. But now you can hear the traffic outside, the kids playing down the street, the dog barking next door etc. Turning the fan off didn’t make these other noise sources louder, but now they are not masked so much and are more annoying. The same thing happens with DACs, as you get rid of one major source of jitter and noise, others now become obvious and they might be harder to get rid of.
Next let’s look at the other inputs to the DAC chip, such as the I2S signals. Those signals might have quite a bit of jitter depending on where they come from. Even though the main clock is supposed to be the arbiter of timing, these other inputs can also affect the internal timing. Each one of those signals has a return current back to wherever it came from, creating ground plane noise to the DAC chip. They also create noise on the internal chip traces from the transistors receiving those signals. All of this creates noise the chip sees whose spectrum is related to the spectrum of the jitter on the I2S signals. So not only is jitter on the master clock important, but so is jitter on the I2S signals. This is important to realize, jitter on ALL input signals to the DAC chip can modify the timing internal to the chip.
So in order to fix this jitter on the I2S signals we “reclock” them with a flip flop clocked by the master clock. BUT the signals going into the flop also cause ground plane noise with a spectrum related to the jitter on the inputs, AND some of the transistors inside the flop are also switching based on the input signals, adding to the ground plane noise correlated to the “jittery” inputs. So why bother reclocking? It DOES decrease jitter, it just doesn’t eliminate it. If the I2S signals have quite a bit of jitter, the reclocking can cut it down by quite a bit, but there is STILL jitter on the output that is correlated to the input jitter AND there is noise on the ground plane related to the input signals that can influence the clock, clock mux, and DAC chip. So while reclocking can help, it is not a panacea.
So now the crux of the matter, how can what goes into the USB receiver affect any of this? In several ways: packet jitter, edge jitter, PLLs. I’ll go over each of these.
Packet jitter is the difference in the arrival time of packets to the receiver chip. USB packets are transmitted over the bus at either 1000 per second (full speed mode) or 8000 per second (high speed mode). Every time one of those packets hits the receiver a lot of activity happens inside the receiver chip. This creates lots of noise inside the chip and on the ground plane. This causes a lot of jitter on the outputs from the chip. The spectrum of this noise and jitter has a VERY strong component at either 1KHz or 8KHz, both of which are directly in the audio range. Any changes in the arrival time of the packets will change the spectrum of this packet noise. In the next installment I’ll cover what causes this packet jitter.
"As with everything else I have been talking about, jitter on the input can cause noise in the chip and on the ground plane that is related to the spectrum of the jitter. This is where things like different cables can have an effect on what is happening."
Next is edge jitter, this is traditional jitter of the individual edges on the bus. As with everything else I have been talking about, jitter on the input can cause noise in the chip and on the ground plane that is related to the spectrum of the jitter. This is where things like different cables can have an effect on what is happening.
Next is PLLs. Every USB receiver chip has at least one if not more PLLs. These PLLs are affected by both the previous types of jitter and since almost all the circuitry inside the chip is clocked by these PLLs, the jitter on output signals and ground plane noise is going to be significantly affected by the noise spectrum coming out of the PLLs. This is filtered by the PLL loop filter, but there are still major components related to the input jitter.
So how do we keep all this noise from the USB receiver from getting to our sensitive DAC circuits? It’s called ground plane isolation. You have separate ground planes for the USB receiver and the rest of the DAC circuitry. This DOES prevent ground plane noise from crossing over. BUT if you cut the ground plane there is no way for the return current from the signals crossing the boundary (the I2S signals and clock etc) to get between the “ground domains”. The solution is digital isolators. There are many different technologies to choose from, one most people are familiar with is opto-couplers. Some of these actually add huge amounts of jitter to the signals going through them so are bad choices for our purposes.
A signal from the receiver now has a return current coming from the isolator so it’s happy. On the other side of the boundary there is a return current to the DAC circuitry so it is happy. BUT any jitter on the signal coming out of the isolator is STILL creating ground plane noise with a spectrum related to the jitter it had on the other side of the isolator. In addition it is containing jitter related to the isolation scheme as well, and some of THAT jitter is ALSO related to noise on the ground plane on the receiver side.
So again the ground plane isolation and signal isolators can decrease the jitter and noise going from the USB receiver to the DAC circuits, BUT they cannot eliminate it. Some always gets through.
"So why even bother with asynchronous USB? Because it DOES help a lot."
So why even bother with asynchronous USB? Because it DOES help a lot. With adaptive USB the clock feeding the DAC chip comes out of the USB receiver with all the rather large amount of noise and jitter already discussed. With async the DAC chip clock does come from a local oscillator, so even though it is affected by the noise from the USB receiver through the mechanisms outlined above, it is still WAY better than what you get out of an adaptive receiver.
You are very much in the scenario I listed above—you have gotten rid of one very large amount of noise, but without it, the affects from other sources are now easily heard. This does not mean the first step was worthless, just not sufficient to completely get rid of it.
Now for some general observations on existing DACs out there “in the wild”. Everything I have discussed here is known. This is not anything new. BUT the number of designers that are familiar with all of this and know how to deal with it are very few. The result is that DACs that deal well with all of these issues are essentially non-existent. Various designers have implemented parts of this in varying degrees, thus there is going to be a wide variation in how different DACs respond to different influences. The upshot is that in the real world of actual DAC implementations there WILL be changes in sound with what is going on outside the DAC box, but it is going to be different for every box, making generalizations about how to make things sound the best, VERY difficult.
Read more at Q&A with John Swenson. Part 2: Are Bits Just Bits? | AudioStream
that cant be right now, can it?
[h=2]Q&A with John Swenson. Part 2: Are Bits Just Bits?[/h]
By Michael Lavorgna • Posted: Aug 28, 2013
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image: http://cdn.audiostream.com/images/styles/600_wide/public/82813js2_0.jpg?itok=ks7UQbMD
Can you explain how things other than "the bits" could have an effect on the analog output of a DAC?
First I’m going to go into some more detail on what I talked about last time, specifically, ramp times. Remember that the jitter caused by the ramp time is a combination of the threshold uncertainty and the ramp time. So it seems at first glance that you can decrease the jitter by having a faster ramp time. Unfortunately it doesn’t work that way.
The same amount of charge needs to be transferred no matter what the ramp time is. So if it takes one half the time, twice as much current has to flow. This causes the ground plane noise to increase, which increases the threshold uncertainty. Thus decreasing the ramp time doesn’t help.
"The result is that faster ramp times actually increase jitter."
It’s actually worse. If you run the “edge” through a Fourier transform (which converts the time domain into a frequency domain) you will see a large amount of very high frequency components. If you decrease the ramp time, those high frequency components increase. When those high frequency currents flow through the inductance in the ground plane they create an even greater voltage drop than already mentioned. The result is that faster ramp times actually increase jitter.
I covered this in detail to show how what seems obvious at first glance may not actually be true when you start dealing with jitter and ground plane noise.
So what about an asynchronous USB interface, isn’t it supposed to completely isolate the DAC from everything? Let’s look in detail at each part of the system and see what affects it.
Let’s start with the local oscillator, the “clock”. It turns out that almost all ultra low jitter oscillators are quite sensitive to ground plane and power supply noise. As the noise increases the jitter increases, and the spectrum of that extra jitter is directly related to the spectrum of the noise. This phenomenon is well known by many digital designers, so many will use decent low noise regulators with the clocks, but many don’t bother with that step, guaranteeing that the low jitter spec of the oscillator is going to be drastically compromised. Not only do you have to deal with the self generated noise of the regulator, but also its ability to block noise coming in on its input supply. Most regulators are very poor at this for high frequencies. This means that noise generated by the other logic elements on the board is going to sail right on through the regulators used in many DACs, causing jitter in the clock whose spectrum is highly correlated to what the rest of the board is doing. It IS possible to do a good job of providing low noise clean power to the clock, but it’s not easy and the designer really has to work at it.
And we still haven’t even talked about the ground plane! The noise on the ground plane is just as important to the jitter of the clock, but it doesn’t have a regulator, it just is what it is. If the clock is going to do what it is supposed to do, the ground plane it is connected to HAS to somehow be isolated from the noise generated by other parts of the circuit. I’ll go into this in detail later on.
So right at the beginning the clock itself is susceptible to influences outside itself in almost all implementations.
After the clocks (it takes two in most implementations) you need a clock mux, which again creates its own jitter from the ground plane noise caused by the return current going back to the clock. In order to decrease this jitter you need to make the ramp time of the clock slow, but not too slow. The adage here is “just fast enough to work in all circumstances”. That means you usually have to slow down the clock edges. Fortunately this is easy to do by just putting a resistor in series with the output. But just this simple little tweak is not done very often. And what about the mux itself? It needs to have the same treatment. Fortunately the designer has a large choice of possible muxes to choose from, some very fast edges and some very slow. As strange as it may seem frequently the best ones to use are the old slow technologies from decades ago. They lumber along with slow edge rates and internal transistors, creating very small amounts of noise. Since the clocks we are talking about here are very slow by modern standards, these old muxes work very well. But again, not many designers take the time to optimize that.
"Most modern DAC chips have a lot of stuff inside creating a lot of noise on the internal power and ground traces, which pretty much nullifies that ultra low jitter clock we are sending it."
Then the clock goes to the DAC chip. Most modern DAC chips have a lot of stuff inside creating a lot of noise on the internal power and ground traces, which pretty much nullifies that ultra low jitter clock we are sending it. This is probably why a large number of people have a hard time hearing differences caused by changes to things such as jitter and noise. The effects caused by them are being swamped by the jitter generated inside the chip.
A number of companies are realizing this and are using DAC chips where a lot of this internal processing can be turned off. This significantly cuts down on internal jitter, BUT it also makes it possible for external influences to be more noticeable. So now the jitter on the main clock fed into the DAC chip starts to be quite important since it’s not masked so much. An analogy might be the noise level in your listening room. Let’s say you have a fan running and you realize that it’s interfering with your enjoyment of the music. So you turn the fan off, expecting perfect quiet. But now you can hear the traffic outside, the kids playing down the street, the dog barking next door etc. Turning the fan off didn’t make these other noise sources louder, but now they are not masked so much and are more annoying. The same thing happens with DACs, as you get rid of one major source of jitter and noise, others now become obvious and they might be harder to get rid of.
Next let’s look at the other inputs to the DAC chip, such as the I2S signals. Those signals might have quite a bit of jitter depending on where they come from. Even though the main clock is supposed to be the arbiter of timing, these other inputs can also affect the internal timing. Each one of those signals has a return current back to wherever it came from, creating ground plane noise to the DAC chip. They also create noise on the internal chip traces from the transistors receiving those signals. All of this creates noise the chip sees whose spectrum is related to the spectrum of the jitter on the I2S signals. So not only is jitter on the master clock important, but so is jitter on the I2S signals. This is important to realize, jitter on ALL input signals to the DAC chip can modify the timing internal to the chip.
So in order to fix this jitter on the I2S signals we “reclock” them with a flip flop clocked by the master clock. BUT the signals going into the flop also cause ground plane noise with a spectrum related to the jitter on the inputs, AND some of the transistors inside the flop are also switching based on the input signals, adding to the ground plane noise correlated to the “jittery” inputs. So why bother reclocking? It DOES decrease jitter, it just doesn’t eliminate it. If the I2S signals have quite a bit of jitter, the reclocking can cut it down by quite a bit, but there is STILL jitter on the output that is correlated to the input jitter AND there is noise on the ground plane related to the input signals that can influence the clock, clock mux, and DAC chip. So while reclocking can help, it is not a panacea.
So now the crux of the matter, how can what goes into the USB receiver affect any of this? In several ways: packet jitter, edge jitter, PLLs. I’ll go over each of these.
Packet jitter is the difference in the arrival time of packets to the receiver chip. USB packets are transmitted over the bus at either 1000 per second (full speed mode) or 8000 per second (high speed mode). Every time one of those packets hits the receiver a lot of activity happens inside the receiver chip. This creates lots of noise inside the chip and on the ground plane. This causes a lot of jitter on the outputs from the chip. The spectrum of this noise and jitter has a VERY strong component at either 1KHz or 8KHz, both of which are directly in the audio range. Any changes in the arrival time of the packets will change the spectrum of this packet noise. In the next installment I’ll cover what causes this packet jitter.
"As with everything else I have been talking about, jitter on the input can cause noise in the chip and on the ground plane that is related to the spectrum of the jitter. This is where things like different cables can have an effect on what is happening."
Next is edge jitter, this is traditional jitter of the individual edges on the bus. As with everything else I have been talking about, jitter on the input can cause noise in the chip and on the ground plane that is related to the spectrum of the jitter. This is where things like different cables can have an effect on what is happening.
Next is PLLs. Every USB receiver chip has at least one if not more PLLs. These PLLs are affected by both the previous types of jitter and since almost all the circuitry inside the chip is clocked by these PLLs, the jitter on output signals and ground plane noise is going to be significantly affected by the noise spectrum coming out of the PLLs. This is filtered by the PLL loop filter, but there are still major components related to the input jitter.
So how do we keep all this noise from the USB receiver from getting to our sensitive DAC circuits? It’s called ground plane isolation. You have separate ground planes for the USB receiver and the rest of the DAC circuitry. This DOES prevent ground plane noise from crossing over. BUT if you cut the ground plane there is no way for the return current from the signals crossing the boundary (the I2S signals and clock etc) to get between the “ground domains”. The solution is digital isolators. There are many different technologies to choose from, one most people are familiar with is opto-couplers. Some of these actually add huge amounts of jitter to the signals going through them so are bad choices for our purposes.
A signal from the receiver now has a return current coming from the isolator so it’s happy. On the other side of the boundary there is a return current to the DAC circuitry so it is happy. BUT any jitter on the signal coming out of the isolator is STILL creating ground plane noise with a spectrum related to the jitter it had on the other side of the isolator. In addition it is containing jitter related to the isolation scheme as well, and some of THAT jitter is ALSO related to noise on the ground plane on the receiver side.
So again the ground plane isolation and signal isolators can decrease the jitter and noise going from the USB receiver to the DAC circuits, BUT they cannot eliminate it. Some always gets through.
"So why even bother with asynchronous USB? Because it DOES help a lot."
So why even bother with asynchronous USB? Because it DOES help a lot. With adaptive USB the clock feeding the DAC chip comes out of the USB receiver with all the rather large amount of noise and jitter already discussed. With async the DAC chip clock does come from a local oscillator, so even though it is affected by the noise from the USB receiver through the mechanisms outlined above, it is still WAY better than what you get out of an adaptive receiver.
You are very much in the scenario I listed above—you have gotten rid of one very large amount of noise, but without it, the affects from other sources are now easily heard. This does not mean the first step was worthless, just not sufficient to completely get rid of it.
Now for some general observations on existing DACs out there “in the wild”. Everything I have discussed here is known. This is not anything new. BUT the number of designers that are familiar with all of this and know how to deal with it are very few. The result is that DACs that deal well with all of these issues are essentially non-existent. Various designers have implemented parts of this in varying degrees, thus there is going to be a wide variation in how different DACs respond to different influences. The upshot is that in the real world of actual DAC implementations there WILL be changes in sound with what is going on outside the DAC box, but it is going to be different for every box, making generalizations about how to make things sound the best, VERY difficult.
Read more at Q&A with John Swenson. Part 2: Are Bits Just Bits? | AudioStream
Audioseduction
Active member
I'm sure glad my DAC dose not depend on the USB power. No need for a device like this for me.
audio.bill
Active member
George - As far as the UpTone Audio REGEN, it has been found to provide a significant improvement in sound quality even with DACs that do NOT use USB power. This is due to regeneration of the USB data signal to improve its signal integrity, which lowers noise in the data recovery circuitry of the signal receiver portion of the DAC. It also improves the impedance matching between the data sender and receiver circuitry which further improves the integrity of the signal.
Audioseduction
Active member
My Bel Canto REFLink Asynchronous USB Converter dose a out standing job for me. I use a ST Optical Glass Fiber to feed the signal to my DAC so the impedance is irrelevant in my case since I'm just sending photons to my DAC. I know the way I pass the signal from my music server to my DAC is very unusual. Not too many people do it exactly the way I do it.
it "may" benefit the converter to have a higher Signal integrity feeding its USB receiver port, as that "may" result in a cleaner conversion to Optical (or it may not). It would be interesting if you could get a loaner to try and let us know.
Certainly your transmission scheme seems very clever!
Certainly your transmission scheme seems very clever!
MusicDirector
New member
- Joined
- May 21, 2013
- Messages
- 2,013
For the love of....!!!!!!!!!!!!!!!!!
I am so sick of politics in everything!!!
My disgust has finally gotten the better of me. The whole industry is sadly becoming a political campaign in some respects.
Here is what I know about this subject:
I don't know why or what the fight is about or really why Mr. Moffat posted what he did or why the whole thing is going on.
I do know via personal experience that Schiit is an upstanding company. I have spoken with reps and Mr. Stoddard several times. Nice folks. Their business model is all about honesty. I was looking for a solution to a PC audio problem and was thinking about getting the Bitfrost. In speaking with the folks at Schiit, they steered me instead to a solution at half the price and did not really discuss the Bitfrost with me much only to say that while it's a fabulous unit like everything else they offer, it would be unnecessary for me to spend that money to solve my problem.
How many companies do we know that willfully and insistantly steer customers towards less costly products, especially in audio? I can count them on one hand.
Every time I have visited their booth at some event not only are they friendly, but they don't push. They are just there to help when needed. If one reads the story of Schiit by Mr. Jason Stoddard (co-founder) one gets every nut and bolt of it. (Also no small feat from Mr. Stoddard either writing all that).
I'm sure the Uptone company also offers good products and everything.
I'm just sick of all the in-fighting and such. I don't know what starts these things, but it's only serving to ruin the industry. I believe lately the industry has a real chance to gain customers in honest fashion, by offering a variety of products to most folks in a wider price range which means bigger audience. An opportunity to purge some of the BS often associated with the industry and provide ways for folks to be satisfied and proud or grateful for their purchase of things that bring them closer to re-engaging with music.
It's because of this lack of engagement to music that we have all the violence and fighting and bad stuff happening all around if you ask me. I think some companies can sort of work together as pointed out subtly by the response from Uptone to bring even more products to market to help more folks get good sound quality which is a essential part of being able to re-engage with music. Why is it we choose to fight instead?
(I'm not even sure I'm keeping the names straight, all I see is red).
Yeah guys, I'm really pissed in a sad way, not a sheer rage or hateful way. I've just run across so much of this stuff lately it has me thinking about leaving all of audio behind in every respect.
~Eric
I am so sick of politics in everything!!!
My disgust has finally gotten the better of me. The whole industry is sadly becoming a political campaign in some respects.
Here is what I know about this subject:
I don't know why or what the fight is about or really why Mr. Moffat posted what he did or why the whole thing is going on.
I do know via personal experience that Schiit is an upstanding company. I have spoken with reps and Mr. Stoddard several times. Nice folks. Their business model is all about honesty. I was looking for a solution to a PC audio problem and was thinking about getting the Bitfrost. In speaking with the folks at Schiit, they steered me instead to a solution at half the price and did not really discuss the Bitfrost with me much only to say that while it's a fabulous unit like everything else they offer, it would be unnecessary for me to spend that money to solve my problem.
How many companies do we know that willfully and insistantly steer customers towards less costly products, especially in audio? I can count them on one hand.
Every time I have visited their booth at some event not only are they friendly, but they don't push. They are just there to help when needed. If one reads the story of Schiit by Mr. Jason Stoddard (co-founder) one gets every nut and bolt of it. (Also no small feat from Mr. Stoddard either writing all that).
I'm sure the Uptone company also offers good products and everything.
I'm just sick of all the in-fighting and such. I don't know what starts these things, but it's only serving to ruin the industry. I believe lately the industry has a real chance to gain customers in honest fashion, by offering a variety of products to most folks in a wider price range which means bigger audience. An opportunity to purge some of the BS often associated with the industry and provide ways for folks to be satisfied and proud or grateful for their purchase of things that bring them closer to re-engaging with music.
It's because of this lack of engagement to music that we have all the violence and fighting and bad stuff happening all around if you ask me. I think some companies can sort of work together as pointed out subtly by the response from Uptone to bring even more products to market to help more folks get good sound quality which is a essential part of being able to re-engage with music. Why is it we choose to fight instead?
(I'm not even sure I'm keeping the names straight, all I see is red).
Yeah guys, I'm really pissed in a sad way, not a sheer rage or hateful way. I've just run across so much of this stuff lately it has me thinking about leaving all of audio behind in every respect.
~Eric
The bottom line is that the Regen definitely improves the sound in most cases (in my system is was a big improvement)and is out selling the Schiit by a wide margin. I have a friend that has the Schiit and it did not improve the sound in his system but it helped with a mismatch between his computer and Schiit DAC.. The Regen and Schiit are 2 different animals.
Indeed Uptone and John are the only ones who did a rather thorough investigation, analysis, prototyping and marketing of a product which specifically deals with frequency optimisation of the PDN noise profile by focusing first and foremost on signal integrity.
The Wyrd doesn't do that at all.
The Regen does have some common parts, like the USB Hub chip, but that chip doesn't by itself resolve the frequency optimisation of the PDN in the USB receiver around the PHY.
The Regen is meant to be used near the DAC, but also has an internal noise profile (less than usual) at its PHY and PDN, so it is susceptible to the SI you feed it, and hence you could even consider feeding the Wyrd (upstream, near the computer) into the Regen to probable good effect.
Aspects of re-clocking and re-generation and clean power have been around a long time.
It is only John whom I've seen explicitly talk about the USB PHY PDN frequency optimisation, and that dates from quite a while as well over at computeraudiophile.com.
The Regen isn't claimed to solve everything (in particular, it isn't itself impervious to SI issues prior to it, it isn't claimed to do full galvanic isolation, it isn't claimed to resolve the remaining issues inherent to the USB Protocol).
But what is does is resolve something which John found to be rather large (in both formal measurements and perceived SQ) when SI is lacking and with the existing USB Receiver PHYs and PDNs. Frequency optimisation of PDNs is a known process: it's already used for high-speed network devices. However, no-one really thought of using the same in audiophile land for USB in consumer-level equipment.
In that sense, this is a very worthwhile innovation.
I2S and other stuff are not relevant to these devices.
FlexibleAudio
Member
Hard to say from afar what happened, but I think it was someone getting slightly too emotional and not calming down before taking to the keyboard. You can probably mingle with this business pressures too I guess. Unfortunately, things stick around on the net and I think it reflects badly on the Wyrd manufacturer...
M
mauidan
Guest
- Thread Author
- #20
How do you know this?