MQN testing/experimentation thread

[sbgk]

Why mqn sd ? I think sq is the best and others report sw as being good, would be interesting to know how these fair in comparison and whether sq does have better timing.

Oh, I haven't kept up with the latest favourite, Gordon - I just picked what I last heard was the best.
I will do a recording of sq & sw now but I expect the plotted differences to be even more subtle than MQN Vs Foobar

Also, remember all these tests are being done with a bog-standard laptop, not an tweaked audio PC

Edit: I don't see a 1024-sq version just sd,sb,sw(all dated 6th Nov) - did you mean sb?

1024 raw background is the sq version, b is byte, w is word, d is double word and q is quadword ie 64 bit, supposed to be as fast as avx instructions.

[jkeny]

1024 raw background is the sq version, b is byte, w is word, d is double word and q is quadword ie 64 bit, supposed to be as fast as avx instructions.

OK, thanks

BTW, I have to correct my misunderstanding of the test - yes, it reveals playback timing errors BUT not specifically between channels rather it is the speeding up/slowing down of the playback of the digital samples.

With a bit of work I'm sure the analysis program software could be modified to analyse/report interchannel timing differences (if there is any)?

[jkeny]

No more interest in this testing, then?
Don't assume my last post about what the test is measuring, means that the test is meaningless - it's measuring the timing errors between playback samples & not the timing errors between channels. But two things can be said about it - it indicates how stable the playback is (down to microsecond level) which is also an indication of the inter-channel timing.

[Diapason]

Purely lack of time on my part. Must try harder!

[jkeny]

Purely lack of time on my part. Must try harder!

Yes, I will be giving you a school report for your parents to read :)

[LowOrbit]

Hi John

I've been converting my dac to pure battery power this weekend and revelling in the results, so not given much thought to this topic.

Next weekend will be busy and off to Brno for a week so it'll be a while before I get time. I want to do some more testing, just need to find some time.

My brief spell with Audacity did throw up one or two little things I want to investigate further, and I want to play with the IQ test also.

Mark

[jkeny]

Hi John

I've been converting my dac to pure battery power this weekend and revelling in the results, so not given much thought to this topic.

Next weekend will be busy and off to Brno for a week so it'll be a while before I get time. I want to do some more testing, just need to find some time.

My brief spell with Audacity did throw up one or two little things I want to investigate further, and I want to play with the IQ test also.

Mark

Cool. Mark, keep at it

[jkeny]

Anybody done any of these IQtest measurements yet or is all this forgotten?

Just to return to perhaps spur someone along this path, here's something that caught my interest:
I saw this post on DIYAudio about measuring VLF noise http://www.diyaudio.com/forums/lounge/2 ... ost3702082

"Hmmm, I have found an interesting way to change the perceived noise, though I am having troubles measuring it.
ARTA running averaging of 2000 or so trials is showing up differences in VLF noise, interestingly.
Subjectively the difference is sort of like reduced jitter/imd, with deeper solider bass and clearer mid/highs.
L/R and depth imaging markedly improved, overall more realistic sound but no FR changes measured. "

VLF (Very Low Frequency) noise is an area I'm interested in & have been following someone else's experiments in this area. His subjective description of the audible changes he hears correlated with the other experimenter & rang some bells with me & with the collective subjective impressions of MQN & also of PS improvement in PCs described in this forum, I believe.

So I looked into Wow & flutter's audibility - this from Wikipedia:

"Wow and flutter are particularly audible on music with oboe, string, guitar, flute, brass, or piano solo playing. While wow is perceived clearly as pitch variation, flutter can alter the sound of the music differently, making it sound ‘cracked’ or ‘ugly’. There is an interesting reason for this. A recorded 1 kHz tone with a small amount of flutter (around 0.1%) can sound fine in a ‘dead’ listening room, but in a reverberant room constant fluctuations will often be clearly heard.[citation needed] These are the result of the current tone ‘beating’ with its echo, which since it originated slightly earlier, has a slightly different pitch. What is heard is quite pronounced amplitude variation, which the ear is very sensitive to. This probably explains why piano notes sound ‘cracked’. Because they start loud and then gradually tail off, piano notes leave an echo that can be as loud as the dying note that it beats with, resulting in a level that varies from complete cancellation to double-amplitude at a rate of a few Hz: instead of a smoothly dying note we hear a heavily modulated one. Oboe notes may be particularly affected because of their harmonic structure. Another way that flutter manifests is as a truncation of reverb tails. This may be due to the persistence of memory with regard to spatial location based on early reflections and comparison of Doppler effects over time. The auditory system may become distracted by pitch shifts in the reverberation of a signal that should be of fixed and solid pitch."

A couple of things jump out at me - these reverberation effects will not be perceived using headphone listening. How many times has this been noted in practise?
The explanation for truncation of reverb trails is interesting!

I'm looking at this in light of the IQtest results I have done & Jim LeSurf's published measurements (remember LeSurf called this Wow & flutter but I think it's better termed Wander) - all of which show differences in VLF (<5Hz), particularly below 1Hz. What these graphs show is that there is a drift in timing (of some 10s of picoseconds, yes picoseconds - if it was differences of microseconds, there would be no question of it's audibility) which span timeframes of 1sec. In other words, measuring timing from second to second, there are differences of timing of some 10s of picoseconds. In real music playback there could be a wander (or phase shift?) in the fades of piano reverb tails. What I would like to establish is how audible resulting phase shifts from this level of timing differences (10s of picoseconds) could be? I see 0.1% of flutter cited above as a small amount which makes me doubt the picoseconds - but I don't give up that easily :) Anybody know of a method of applying wander (low frequency) to actual recordings down to the picosecond level in order to establish it's audibility or otherwise? I know this timing is orders of magnitude off what seems to be audible but I was just like to satisfy myself that there aren't some secondary effects resulting from these picosecond fluctuations that are audible i.e the effects of room reflections

Again, this may be grasping as straws :) to find differences but I can see a correlation (the lower VLF measurements map to better SQ) here between the recordings made direct from laptop out Vs via USB to Ciunas DAC. And again I can see the same SQ correlation between measurements made using Foobar Vs MQN.

I also wonder if maybe the differences in these measurements are indirectly signifying an underlying difference in low frequency noise?

It's only with a larger body of such correlating measurements would it signify a worthwhile avenue of investigation to follow!

Come on, guys! Have a go!

[jkeny]

More from DIYAudio http://www.diyaudio.com/forums/analog-l ... ost3689373
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1/f Noise Is The Devil....
Reducing very low frequency system noise (<< 20 Hz) by only a couple or few dB reduces a layer of intermod that intrudes over everything in the band of interest (20-20k).

This effective system intermod behaviour of 1/f noise is also spectrally important..ie the nature of the VLF noise imparts a signature/character to the noise/distortion floor.

IME this is a big arbiter of perceived noise/distortion floor, and further affects/effects all standard descriptions of sound quality...ie overall clarity of sound, L/R separation, depth perception etc.....focus, rhythm, timing etc.
When very low frequency noise reduction is applied to both channels coherently, the perceived noise drops further, thus enabling further improved focus, low level detail, and depth information retrieval.

System intermod behaviour also increases/enables/causes audibilty of low frequency noises, so any reduction/change in VLF system noise would serve to reduce/change 'groove' noise.

I expect the Bybee devices are changing VLF noise level/behaviour/spectrum.....not by a lot, but enough to cause an audible difference.

Dan.

[Diapason]

I still hope to get around to looking at some of your files, John, but time has eluded me. All very interesting, though!