MQN testing/experimentation thread

[jesuscheung]

Simply send the data out of the computer and feed it to a dac, capture the output of the dac. As long as you use the same signal chain for both files, you are good to go.

It's not a waveform until it goes through the dac.

If you want to examine the digital domain you need a whole host of software mods (and then, as you say, you are interfering in what you are trying to measure, screwing with your results) or some very fancy test equipment. Personally I am interested in what is different in the analogue signal that emerges from the dac from one player to another (same computer, same cables, same dac, only player is different).

don't understand. MQn goes from disk to memory to WASAPI to DAC. you saying you are streaming data from LAN cable to another computer's DAC? that's not part of the audio path. you need to measure what actually just happened.

[jkeny]

PS jkeny - if you use a recorder in the measurement process, surely that is introducing an unknown and potentially unreliable step in the measurement chain?

Yes, I mentioned this as an area that needs to be carefully controlled.
the things that need to be addressed with this is:
- ensure that the AD converter in the recorder is sufficiently accurate & sensitive enough that it is capable of capturing what we are trying to measure. The problem here is that we don't know what level we need to be able to record to.
- We have to ensure the reliability of the recorder by doing repeatable recordings at various levels
- we effectively have to have controls which prove that the measurement technique can reliable uncover
- the final point is that we are measuring the analogue output from a DAC - this is the signal (amplified) that we are hearing differences in. So even though I would be interested in finding/measuring differences further up the signal chain i.e in the USB signal coming out of the PC, this would leave open the question that timing differences before the DAC would be dealt with by reclocking within the DAC & therefore not an issue.

BTW, the same objection will be levied at any differences that might be found, noise, etc - the objection being that these are only a problem when using a badly designed DAC i.e one that doesn't isolate itself from the noise coming down the USB cable

Remember, regarding jitter there are two "objector" groups & the same will occur here if any differences are found
- one group who claim that modern, competent DACs, reduce incoming jitter to inaudible levels
- one group who claim that high nanoseconds of jitter are only barely audible & this is no longer an issue with modern digital equipment

So don't expect universal acceptance even if differences are found

[DaveF]

I've been away for the last couple of weeks so just catching up on the last few pages.

Even if we manage to come up with a valid and repeatable measuring technique, we're still only gonna be measuring at the output of the DAC or amp. We musnt forget that we have the additional stage of the electronic crossover in the speaker and the mechanical responses of the driver/cones.
I guess my point is that even if we managed to find differences within the noise of different MQNs, they could well be "swallowed up" or not revealed by the speaker thus making them inaudible. Now I dont know much about proper speaker design but I'm guessing that ideally a very accurate studio monitor would be required here.

The ultimate solution would be to somehow measure at the speaker output but as a starting point, measuring at the DAC is probably easier.

Edit: I really dont like the idea of using a recorder. That itself may well 'spoil' the data recorded and introduce its own noise, phase distortions, freq rolloff/gain and god knows what else.
A non intrustive measuring technique is the goal if possible.

[LowOrbit]

Simply send the data out of the computer and feed it to a dac, capture the output of the dac. As long as you use the same signal chain for both files, you are good to go.

It's not a waveform until it goes through the dac.

If you want to examine the digital domain you need a whole host of software mods (and then, as you say, you are interfering in what you are trying to measure, screwing with your results) or some very fancy test equipment. Personally I am interested in what is different in the analogue signal that emerges from the dac from one player to another (same computer, same cables, same dac, only player is different).

don't understand. MQn goes from disk to memory to WASAPI to DAC. you saying you are streaming data from LAN cable to another computer's DAC? that's not part of the audio path. you need to measure what actually just happened.

JC - think you misunderstood me. I never mentioned lan. The signal path Player - Wasapi - Driver Buffer - USB - Out is the same whichever player is used. So Computer - Dac - Capture Device. We are talking about the same thing.

[LowOrbit]

I've been away for the last couple of weeks so just catching up on the last few pages.

Even if we manage to come up with a valid and repeatable measuring technique, we're still only gonna be measuring at the output of the DAC or amp. We musnt forget that we have the additional stage of the electronic crossover in the speaker and the mechanical responses of the driver/cones.
I guess my point is that even if we managed to find differences within the noise of different MQNs, they could well be "swallowed up" or not revealed by the speaker thus making them inaudible. Now I dont know much about proper speaker design but I'm guessing that ideally a very accurate studio monitor would be required here.

The ultimate solution would be to somehow measure at the speaker output but as a starting point, measuring at the DAC is probably easier.

Dave

Ignore the amps and speakers and room. They would be the same (in any given system) whichever player we used. And - allowing that we do hear a difference between playback software versions - we can assume the speakers are good enough to let that difference through.

Capturing at the DAC output removes any speaker/room issues and also removes any possible issues of microphone placement, background noise, power amplifier distortion and so on.

Mark

[jkeny]

Dave

Ignore the amps and speakers and room. They would be the same (in any given system) whichever player we used. And - allowing that we do hear a difference between playback software versions - we can assume the speakers are good enough to let that difference through.

Capturing at the DAC output removes any speaker/room issues and also removes any possible issues of microphone placement, background noise, power amplifier distortion and so on.

Mark

Yes, Mark, I agree.
Given that MQN has already had some blind tests & we can all hear differences, I think that we can be happy with this aspect. Some further blind testing would not hurt, I'm sure but measurements are the sine qua non next step.

I'm wondering if we don't need to approach measuring noise at very low levels in a lateral, less direct way - something along the lines of how the IQtest works for timing? IQtest works because it uses a pre-created signal that has a specific timing between each sample pair & the output signal can then be analysed for this same timing ratio at each point.

DaveF makes a good point - the added noise of the DAC, recording equipment, cables, etc. which we have to separate from the noise we want to examine. I guess one way to address this is to do a recording of 0dB signal, if that's possible (some recorders will not do this). But do we playback 0dB signal & record it with various software players & then do a comparison of the recorded signal? I guess the first stage is to record the DAC output of a song played back using MQN & compare it to the same song played back using Foobar or a different version of MQN. Attempting to Null the recorded file against the original file should reveal any noise, I believe.

Unfortunately we can't create one channel of noise & one of anti-noise that when combined cancel out perfectly.

[LowOrbit]

Hi John

I think that would be a good step - I think we may need to try as many of the proposed approaches, see which yields the clearest, repeatable result. Using a predefined test signal (a la IQTest) is a valid approach, though it may take some fiddling with waveform/samplerate to get something that reveals anything (a simple sinewave may not yield much information unless we use a very high pitched tone). Maybe a Triangle wave at 10khz (as long as it doesn't have to come out of my speakers at any volume!)

(Incidentally we might be able to create a noise/anti-phase left/right stereo signal in a software synth or DAW - I'll give it some thought. I have a fair bit of such software.)

Mark

[jkeny]

Hi John

I think that would be a good step - I think we may need to try as many of the proposed approaches, see which yields the clearest, repeatable result. Using a predefined test signal (a la IQTest) is a valid approach, though it may take some fiddling with waveform/samplerate to get something that reveals anything (a simple sinewave may not yield much information unless we use a very high pitched tone). Maybe a Triangle wave at 10khz (as long as it doesn't have to come out of my speakers at any volume!)

Yes, a lateral approach may yield better results than a direct null of a music signal. BTW, we are leaving out the amp & speakers, right? Don't need to include this - it would make impossible noise measurement at a low enough signal level.

(Incidentally we might be able to create a noise/anti-phase left/right stereo signal in a software synth or DAW - I'll give it some thought. I have a fair bit of such software.)

Mark

Right, I was wondering if we could do this but white noise is at all frequencies so there can't be anti-phase noise, can there?

[jkeny]

BTW, it might be worth reading this thread on PeterSt's forum (He of XXhighend & NOS1 DAC fame) "Hunting for noise" http://www.phasure.com/index.php?topic= ... 0#msg27390

I always find his english difficult to understand particularly when technical matters are being talked about so I will give this another try but if anyone gets any inspiration from it let us know here?

[jrling]

Saw this article over on CA (sorry SBGK!) -
http://www.computeraudiophile.com/conte ... omparison/

Mitch was using readily available tools to do pretty much what we would want to do with MQn by the looks of it. However all in the digital domain and perhaps therefore beyond the limits of the software to detect minute differences? He was comparing JRiver on Windows with JRiver on Mac so perhaps there are actually no differences in that comparison.

Anyone think his approach would work for our experiments?

Jonathan

Sorry if I am being a bit dim, (again!), but isn't jkeny's suggestion very much the same as this approach by Mitch? Although he uses a real music file which one would think is more valid than a test file. It does use readily available software which LowOrbit may already have?