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Jitter problem


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Hi, I have a jitter problem.

 

I stream digital audio from a (notebook) PC directly via WASAPI through a USB 2.0 connection into an (asynchronous) Musical Fidelity MX-DAC and a good quality sound system. That should give me bit-perfect data transfer and good quality overall sound reproduction. However, using a calibrated microphone and sound analysis software, I measure massive amounts of jitter when I play a 16/44.1 pseudo-noise test track from the PC, using Foobar2000 in exclusive (WASAPI) modus.

 

When I play the exact same test track on a good quality CD-player which is optically (toslink) connected to the same DAC and sound system, then there’s no measurable jitter at all. In fact, the measured amount of jitter which is apparently coming from the PC/driver/USB connection, is practically the same with the MX-DAC as it is with a relatively simple synchronous CYP AU-D150 DAC that I also have.

 

Now, it seems that either jitter elimination by the MX-DAC through asynchronous buffering and reclocking of the incoming (USB) data stream doesn’t work as advertised, or Foobar2000 WASAPI direct modus doesn’t quite produce a bit-perfect stream (i.e., the exact bits irrespective of timing errors). Could actual audio processing timed by the PC-clock still be going on somewhere :eek:, or do I need another DAC to stream audio from a PC?

 

I’m fairly new to computer audio and streaming music from the internet. I see it has huge potential but I really want it to sound at least as good as my old redbook CDP. Any ideas? Thanks.

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First thing first: you are not measuring jitter. That is done in the digital domain. Care to post your measurements?

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Hi Freann,

 

It is possible to measure the effect of jitter in the analogue/audible domain by using noise. Basically, noise can have a frequency spectrum such that the energy is equal per Hz (white noise) or the energy is (e.g.) inversely proportional to frequency (pink noise). Timing errors (jitter) in the digital domain will selectively degrade higher frequencies in a decoded analogue noise signal. Digital timing errors lead to (small) phase-shifts in the decoded analogue signal. Contrary to a pure sine signal or a sine sweep, which contains only a single frequency at any time, such phase-shifts in noise will result in higher frequencies cancelling each other out, which shows up as lower energy (SPL) in a frequency response plot based on a Fourier-analysis of the frequency spectrum of the audible noise signal, relative to a regular frequency response plot based on a pure sine sweep.

 

I will post the measurements tomorrow. For now, significant high frequency degradation/cancellation in noise resulting from jitter coming from the PC starts at around 10kHz (1dB) and increases to over 10dB (!) at 15kHz and higher. The same measurements show no high frequency degradation when the noise signal is burned on a regular CD and played by the CD-player.

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Aha, did not know. Looking forward to the measurements.

Roon client on iPad/MacBookPro

Roon Server & HQPlayer on Mac Mini 2.0 GHz i7 with JS-2

LPS-1 & ultraRendu → Lampizator Atlantic → Bent Audio TAP-X → Atma-sphere M60 → Zero autoformers → Harbeth Compact 7 ES-3

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Here are the measurement results. The first graph shows the FR from the PC with the blue curve representing the FR from a sine sweep and the red curve representing the FR from noise. It can be seen that frequency cancelation even starts at 2kHz! The second graph shows the same measurements for the CD-player (with the same MX-DAC). Here the two curves are identical. There’s no frequency dependent cancellation and thus no jitter.

 

CDP.png

 

By the way, I tried the AudioQuest Jitterbug (in fact, the PC measurements were made with a Jitterbug) but it doesn’t appear to reduce the cancellation/jitter, although music seems to slightly 'open up' with the Jitterbug in place (?). I’m thinking of trying the Upsound Regen. I read about it on this forum and possibly it will cure the problem. As it is, I can’t really enjoy streaming audio from my PC.

PC.png

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Is that -12 dB? That’s eye opening. Considering jitter is measured in picto seconds.

Roon client on iPad/MacBookPro

Roon Server & HQPlayer on Mac Mini 2.0 GHz i7 with JS-2

LPS-1 & ultraRendu → Lampizator Atlantic → Bent Audio TAP-X → Atma-sphere M60 → Zero autoformers → Harbeth Compact 7 ES-3

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Does it sound OK? Did you take measurements just out of curiosity, or is there some kind of problem?

I suppose the sound would qualify as 'hifi' and the noise signal used for the measurements actually exaggerates the effect of jitter in the 44.1kHz domain relative to the effect it has on music. But music sounds dull and liveless and less spacious relative to what my redbook CDP (Arcam FMJ CD23T) manages to produce.

 

Are you able to record the analogue output of the DAC directly rather than using a mike? It also might be informative to try with the j-test signal usually used for jitter measurements.

I will look into that..

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I suppose the sound would qualify as 'hifi' and the noise signal used for the measurements actually exaggerates the effect of jitter in the 44.1kHz domain relative to the effect it has on music. But music sounds dull and liveless and less spacious relative to what my redbook CDP (Arcam FMJ CD23T) manages to produce.

 

 

I will look into that..

 

That's interesting. Arcam CD players share a similar house sound. I have a 33 myself. I use it on poor recordings because it sounds fairly smooth and forgiving. Most of the same recordings played one of my Wadia's is hard to listen to because they have more detail and are less forgiving. So, when you say that your PC setup sounds dull and lifeless compared to the Arcam, I can see why you're concerned.

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That's interesting. Arcam CD players share a similar house sound. I have a 33 myself. I use it on poor recordings because it sounds fairly smooth and forgiving. Most of the same recordings played one of my Wadia's is hard to listen to because they have more detail and are less forgiving. So, when you say that your PC setup sounds dull and lifeless compared to the Arcam, I can see why you're concerned.

I know what you mean and the CD23 and CD33 are essentially the same player (although the 23 has the dCS ring dac whereas the 33 uses a Wolfson dac). However, the smooth character of the Arcam cannot be the issue here. I currently use the player only as a transport, connected via toslink with the Musical Fidelity MX-DAC which I prefer over the dCS ring-dac (wider an deeper soundstage, better detail and imaging, tighter and seemingly deeper bass). The PC is also connected to the MX-DAC through USB. So, the measured and perceived difference between PC and CDP transport is not the DAC.

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Did you try to change the player? Are there any differences between players like jriver or foobar?

 

Wouldn't make a difference, at least it did not for me.

 

No. Good point. I will try JRiver. Running Foobar in direct mode didn't improve things which makes me wonder whether Foobar is actually running in direct (WASAPI) mode..

 

You can try playing something else on the browser via YouTube or another player like VLC or JRiver. At least if the sound device is common then you'd get an error if Foobar was using it in WASAPI mode.

 

I'd simply dispense with USB and go with optical Toslink or Coaxial. That's one option to seriously consider with digital.

Next to the Word of God, the noble art of music is the greatest treasure in the world - Martin Luther

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I'd simply dispense with USB and go with optical Toslink or Coaxial. That's one option to seriously consider with digital.

 

Preferably from a good soundcard though, NOT Motherboard Optical.

 

How a Digital Audio file sounds, or a Digital Video file looks, is governed to a large extent by the Power Supply area. All that Identical Checksums gives is the possibility of REGENERATING the file to close to that of the original file.

PROFILE UPDATED 13-11-2020

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I know what you mean and the CD23 and CD33 are essentially the same player (although the 23 has the dCS ring dac whereas the 33 uses a Wolfson dac). However, the smooth character of the Arcam cannot be the issue here. I currently use the player only as a transport, connected via toslink with the Musical Fidelity MX-DAC which I prefer over the dCS ring-dac (wider an deeper soundstage, better detail and imaging, tighter and seemingly deeper bass). The PC is also connected to the MX-DAC through USB. So, the measured and perceived difference between PC and CDP transport is not the DAC.

 

Have you tried using Toslink from the PC?

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Here are the measurement results. The first graph shows the FR from the PC with the blue curve representing the FR from a sine sweep and the red curve representing the FR from noise. It can be seen that frequency cancelation even starts at 2kHz! The second graph shows the same measurements for the CD-player (with the same MX-DAC). Here the two curves are identical. There’s no frequency dependent cancellation and thus no jitter.

 

[ATTACH=CONFIG]24642[/ATTACH][ATTACH=CONFIG]24643[/ATTACH]

 

By the way, I tried the AudioQuest Jitterbug (in fact, the PC measurements were made with a Jitterbug) but it doesn’t appear to reduce the cancellation/jitter, although music seems to slightly 'open up' with the Jitterbug in place (?). I’m thinking of trying the Upsound Regen. I read about it on this forum and possibly it will cure the problem. As it is, I can’t really enjoy streaming audio from my PC.

 

I'm not sure I would trust your test as valid unless you can show matching improvement from applications that are known to reduce PC OS cycle stealing jitter. Please try running Fidelizer to see if your measured "jitter" reduces. I would not be surprised if you are hearing jitter injected before signal ever reaches USB port.

Regards,

Dave

 

Audio system

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I'm not sure I would trust your test as valid unless you can show matching improvement from applications that are known to reduce PC OS cycle stealing jitter. Please try running Fidelizer to see if your measured "jitter" reduces. I would not be surprised if you are hearing jitter injected before signal ever reaches USB port.

 

If anything is altering the PCM data between the player and the DAC it's deliberate. The question is what's doing it, and to determine that, the first step is to make sure the playback really is bit perfect, i.e. any mixing, resampling, equalisation, or similar in the drivers must be bypassed (WASAPI).

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If anything is altering the PCM data between the player and the DAC it's deliberate. The question is what's doing it, and to determine that, the first step is to make sure the playback really is bit perfect, i.e. any mixing, resampling, equalisation, or similar in the drivers must be bypassed (WASAPI).

 

It is deliberate... it's called Operating System architecture. Hence why many prefer Mac and Linux machines for audio.

Regards,

Dave

 

Audio system

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Have you tried using Toslink from the PC?

None of my PCs have coaxial or Toslink outputs. I might try a good soundcard that has..

 

I'm not sure I would trust your test as valid unless you can show matching improvement from applications that are known to reduce PC OS cycle stealing jitter. Please try running Fidelizer to see if your measured "jitter" reduces. I would not be surprised if you are hearing jitter injected before signal ever reaches USB port.

The 'test' is valid, and basically my CD transport is an 'application' known to produce virtually no jitter which is clearly demonstrated in the second graph. I may try Fidelizer, thanks, but WASAPI should bypass any (other) sound processing software that may be active on the PC.

 

 

Regarding Foobar's exclusive (WASAPI) mode: when Foobar is running in exclusive mode, then the Tidal desktop application (also running in exlusive mode) crashes and Windows Media Player produces an error. So, Foobar appears to be running in exlusive mode.. And I ordered an Intona USB Isolator :) It is advertized to do some serious high speed USB reclocking which may/should reduce or even eliminate the 'jitter problem'.

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I know what you mean and the CD23 and CD33 are essentially the same player (although the 23 has the dCS ring dac whereas the 33 uses a Wolfson dac). However, the smooth character of the Arcam cannot be the issue here. I currently use the player only as a transport, connected via toslink with the Musical Fidelity MX-DAC which I prefer over the dCS ring-dac (wider an deeper soundstage, better detail and imaging, tighter and seemingly deeper bass). The PC is also connected to the MX-DAC through USB. So, the measured and perceived difference between PC and CDP transport is not the DAC.

 

Sorry. Your other post made it look like you were comparing your PC setup directly to your 23.

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Andyou think that Foobar and WASAPI have total control of the PC environment? Ilike Foobar but Fidelizer or Jplay were necessary for PC playback to soundbetter than a table radio

Hi David,

 

A typical Windows PC has many simultaneous processes (programs and services) running in thousands of threads. Reducing the number of processes to a minimum and raising the priority of audio-processes, will minimize the number of OS interrupts of audio processing which will reduce timing errors (jitter) in the audio stream. Fidelizer, XXhighend, Jplay, etc. do just that and this will improve sound for simple adaptive USB.

 

However, irrespective of any degree of interruption and timing errors, WASAPI should produce a bit perfect stream. And by design (through buffering and reclocking) asynchronous USB allows for very low intrinsic jitter. Hence, my initial surprise that the Musical Fidelity MX-DAC's asynchronous USB implementation doesn't eliminate (all) jitter from the audio signal. But I now think that the timing errors are thus pervasive that the DAC just can't keep up in which case Fidelizer could actually improve things. Nevertheless, the Intona USB Isolator that I ordered may do a much better job of reclocking the audio stream, which will hopefully make all such optimizations an tweaks unnecessary. We'll see..

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