Bit-identical playback CAN sound different

[manisandher]

I've noticed that there have been a few references recently to my 'Blue or red pill?' thread:

 

I really have no interest in repeating the test. If you believe that all bit-identical playback sounds the same, then more power to you. You're delluded I'm afraid, but at least you've saved yourself a lot of time and effort in optimising your playback chain.

 

But recent mention of the test prompted me to do a quick follow-up. I captured the output from the speakers in my office, using the two exact same bit-identical settings we used in the test. Here's the replay/record chain I used:

 

XXHighEnd -> USB -> RME ADI-2 Pro FS R (as DAC) -> balanced XLR -> First Watt F4 mono amps -> Tune Audio Marvel speakers -> Rode NT4 stereo mic (~3m from speakers) -> MOTU M2 ADC -> Audacity (24/48)

 

And here are the two files:

 

Take 1: https://drive.google.com/file/d/1pA6Wq67q8Nh7csC-iuA2lN4k-JZR0wT_/view?usp=sharing

Take 2: https://drive.google.com/file/d/17UXfLQtKLqunanHsE9NTlIDIVl9ZppXE/view?usp=sharing

 

If you can't hear a difference... sleep well at night. If you can... you've swallowed the red pill 😉.

 

Mani.

[manisandher]

DeltaWave shows the main difference between the two mic captures as lying between 16-20kHz:

 

 

This is just one data point of course. At some point, I'll take a number of captures at both settings to see if there is a consistent difference.

 

Mani.

[pkane2001]

8 minutes ago, manisandher said:

DeltaWave shows the main difference between the two mic captures as lying between 16-20kHz:

 

 

This is just one data point of course. At some point, I'll take a number of captures at both settings to see if there is a consistent difference.

 

Mani.

 

 

Hi Mani,

 

I'm trying to install XXHighEnd myself :) I need a lot of help getting it configured the right way -- the UI isn't easy to navigate, and appears to not size properly on my Windows 7 computer.

 

Right now it's playing the files I ask, but appears to be 1dB below the volume level I've configured. Hard to tell, but am I missing some setting that's causing this?

[pkane2001]

7 minutes ago, pkane2001 said:

Right now it's playing the files I ask, but appears to be 1dB below the volume level I've configured. Hard to tell, but am I missing some setting that's causing this?

 

Figured it out, it was the oversampling option. When turned off, the level is correct.

 

[manisandher]

I was just replying... but now no need to 🙂.

 

Let me know if there's anything else I can help with.

[manisandher]

I'll try to take more mic captures when the boys are asleep... and the wife's not blasting the TV in the living room 😉.

[fas42]

Thanks for that - yes, it's obvious ... a simple tell: listen to the quality of the "ss'es" in the vocal, between the two. Transients are much better defined, in one of them.

[sandyk]

1 hour ago, fas42 said:

Thanks for that - yes, it's obvious ... a simple tell: listen to the quality of the "ss'es" in the vocal, between the two. Transients are much better defined, in one of them.

Yes, the differences are quite obvious, especially in the area of ingrained noise, however the conversions are no longer Bit Perfect.

 

P.S. 

In this thread, Digital Signal Transmission - Page 9 - Objective-Fi - Audiophile Style

the OP (TomJ) quietly disappeared into the void after a PM reply, but with without further posting, after he heard differences between Bit Perfect .wav files for himself, just as another Objective poster did after hearing the same differences as Frank reported with the same files.

 

[manisandher]

6 hours ago, sandyk said:

... however the conversions are no longer Bit Perfect.

 

Sorry Alex, I don't understand what you mean.

 

Mani.

[PeterSt]

13 hours ago, pkane2001 said:

appears to not size properly on my Windows 7 computer.

 

Might it help :

 

 

You can size and Skin about everything individually. See the [S] button in the main screen.

 

Also notice that the [1] button in the top, implies a separator bar :

 

 

When not dragged sufficiently to the right, this part will be not in view :

 

 

[sandyk]

2 hours ago, manisandher said:

 

Sorry Alex, I don't understand what you mean.

 

Mani.

By that, I mean that because the captured microphone recordings are not bit perfect, this means that you should also also include the  original captured identical .wav files for transparency. 

[PeterSt]

1 minute ago, sandyk said:

this means that you should also also include the  original captured identical .wav files for transparency. 

 

so you can run a checksum over it, right ?

hahaha

 

I am not Mani. But let's have both feet on the ground for once. All of us. Just have fun. And assume that nobody is fooling. Or making mistakes.

[sandyk]

29 minutes ago, PeterSt said:

 

so you can run a checksum over it, right ?

hahaha

 

I am not Mani. But let's have both feet on the ground for once. All of us. Just have fun. And assume that nobody is fooling. Or making mistakes.

Come on Peter, you well know the attitude of a few no longer here Objective members especially. 😜

 

 I feel sure that a few would also have liked the opportunity to listen to the original bit perfect versions now that the microphone captures are making them obvious to some of us at least 

Perhaps Frank included, who is no longer new to actually  hearing these supposedly impossible happenings for himself ?

[manisandher]

1 hour ago, sandyk said:

By that, I mean that because the captured microphone recordings are not bit perfect, this means that you should also also include the  original captured identical .wav files for transparency. 

 

Alex, I don't think bringing up the term 'bit-perfect' is at all useful here.

 

The two microphone captures are of a file being played back in two bit-identical ways. With just a simple listen, one should be able to determine whether they sound different or the same. If they sound different, then we can start asking why that might be. The DAC is a well-regarded professional unit with excellent measurements. And yet, without changing the bits reaching it at all, we can change its sound.

 

Nice and simple.

 

Mani.

[pkane2001]

2 hours ago, PeterSt said:

 

Might it help :

 

 

You can size and Skin about everything individually. See the [S] button in the main screen.

 

Also notice that the [1] button in the top, implies a separator bar :

 

 

When not dragged sufficiently to the right, this part will be not in view :

 

 

 

The interface certainly takes some getting used to, but I think I figured out how to get the basic functionality to work now, thanks Peter!

 

[sandyk]

26 minutes ago, manisandher said:

With just a simple listen, one should be able to determine whether they sound different or the same. If they sound different, then we can start asking why that might be

Mani

I am more here about Dotting the  " i  " and Crossing the "t" for the sceptics such as Mansr etc. who will always find some excuse to refuse to accept the results of anything their grasp of Theory does not agree with.

G'night

Alex

[pkane2001]

20 hours ago, manisandher said:

I've noticed that there have been a few references recently to my 'Blue or red pill?' thread:

 

I really have no interest in repeating the test. If you believe that all bit-identical playback sounds the same, then more power to you. You're delluded I'm afraid, but at least you've saved yourself a lot of time and effort in optimising your playback chain.

 

But recent mention of the test prompted me to do a quick follow-up. I captured the output from the speakers in my office, using the two exact same bit-identical settings we used in the test. Here's the replay/record chain I used:

 

XXHighEnd -> USB -> RME ADI-2 Pro FS R (as DAC) -> balanced XLR -> First Watt F4 mono amps -> Tune Audio Marvel speakers -> Rode NT4 stereo mic (~3m from speakers) -> MOTU M2 ADC -> Audacity (24/48)

 

And here are the two files:

 

Take 1: https://drive.google.com/file/d/1pA6Wq67q8Nh7csC-iuA2lN4k-JZR0wT_/view?usp=sharing

Take 2: https://drive.google.com/file/d/17UXfLQtKLqunanHsE9NTlIDIVl9ZppXE/view?usp=sharing

 

If you can't hear a difference... sleep well at night. If you can... you've swallowed the red pill 😉.

 

Mani.

 

Hi Mani, 

 

Here are some more interesting measurements from the two files:

 

The thing that's interesting above is the difference below 75Hz or so. Also, not that it should be audible (maybe through IMD?), but there's some noise above 19kHz:

 

 

PK Metric also shows some areas of concern:

 

[yamamoto2002]

For control experiment, it is nice to have two recorded data of the same file

[manisandher]

Thanks Paul

 

32 minutes ago, pkane2001 said:

The thing that's interesting above is the difference below 75Hz or so.

 

I wouldn't be inclined to read too much into this. Our front drive is a few meters away from a main road and it may well be that a lorry just happened to have passed by during one of the takes.

 

32 minutes ago, pkane2001 said:

Also, not that it should be audible (maybe through IMD?), but there's some noise above 19kHz:

 

This is what caught my eye immediately. The noise shows up on the capture with XXHighEnd SFS=0.69. Generally, the lower the SFS setting the 'sharper' the sound. Perhaps due to noise?

 

32 minutes ago, pkane2001 said:

PK Metric also shows some areas of concern:

 

What exactly does the 'PK Metric' show?

 

I obviously need to take more measurements to eliminate random occurrences...

 

Mani.

[manisandher]

9 minutes ago, yamamoto2002 said:

For control experiment, it is nice to have two recorded data of the same file

 

Yep. And I'll get around to doing more recordings.

 

Mani.

[pkane2001]

14 minutes ago, manisandher said:

Thanks Paul

 

 

I wouldn't be inclined to read too much into this. Our front drive is a few meters away from a main road and it may well be that a lorry just happened to have passed by during one of the takes.

 

 

This is what caught my eye immediately. The noise shows up on the capture with XXHighEnd SFS=0.69. Generally, the lower the SFS setting the 'sharper' the sound. Perhaps due to noise?

 

 

What exactly does the 'PK Metric' show?

 

I obviously need to take more measurements to eliminate random occurrences...

 

Mani.

 

Yeah, the noise above 19kHz is persistent through the whole recording, and it's about 10dB in magnitude, so not tiny.

 

PK Metric attempts to apply perceptual weights to the difference signal. It takes into account equal loudness curves, so that both, the level and the frequency of the error drive the magnitude, and then also uses ERB smoothing to compensate for errors that occur close enough in frequency to be masked by the main signal. In effect, it helps with audibility determination, as well as, shows where in the file the error is likely to be more audible (peaks, like the one around 8-9 second mark and then above 11 secs). 

[manisandher]

28 minutes ago, pkane2001 said:

Yeah, the noise above 19kHz is persistent through the whole recording, and it's about 10dB in magnitude, so not tiny.

 

That doesn't sound too promising to me. The MOTU M2 is connected to the regular work PC on my desk. Although passively cooled for the most part, it does have a couple of fans in its graphics card which are just about audible when the room is otherwise silent. I wonder if the HF noise comes from these fans - maybe they ramped up during one of the takes? Easily checked - I'll take a few recordings of the ambient room noise.

 

If necessary, I can plug the M2 into my totally passive laptop for further mic captures.

 

35 minutes ago, pkane2001 said:

PK Metric attempts to apply perceptual weights to the difference signal. It takes into account equal loudness curves, so that both, the level and the frequency of the error drive the magnitude, and then also uses ERB smoothing to compensate for errors that occur close enough in frequency to be masked by the main signal. In effect, it helps with audibility determination, as well as, shows where in the file the error is likely to be more audible (peaks, like the one around 8-9 second mark and then above 11 secs). 

 

Thanks.

 

Playing either track back through DeltaWave, two things occur to me:

 

1. the leading edges of the guitar plucks coincide perfectly with the peaks in the PK Metric curve

2. the leading edges of the guitar plucks clearly sound softer on one of the tracks than the other (in exactly the way any XXHighEnd user would expect)

 

As I've said, I'll take more captures with the mic...

 

Mani.

[danadam]

1 hour ago, manisandher said:

What exactly does the 'PK Metric' show?

https://deltaw.org/pk_metric.html

 

56 minutes ago, pkane2001 said:

In effect, it helps with audibility determination, as well as, shows where in the file the error is likely to be more audible

Doesn't work too well for me :-) Can't say I hear anything different at 8-9 or 11 seconds. I do hear a clear difference at 32.5 seconds, which is rather not surprising:

 

I also hear the difference at 1 second:

 

[yamamoto2002]

34 minutes ago, manisandher said:

 

That doesn't sound too promising to me. The MOTU M2 is connected to the regular work PC on my desk. Although passively cooled for the most part, it does have a couple of fans in its graphics card which are just about audible when the room is otherwise silent. I wonder if the HF noise comes from these fans - maybe they ramped up during one of the takes? Easily checked - I'll take a few recordings of the ambient room noise.

 

If necessary, I can plug the M2 into my totally passive laptop for further mic captures.

 

That 19kHz noise may be inductor whine, move microphone to close to any switching power supply or DC-DC converter (PC, network switch, monitor display, graphics board, LED lamps etc) and see what device emit the noise :)

 

 

[manisandher]

9 minutes ago, danadam said:

Can't say I hear anything different at 8-9 or 11 seconds.

 

Listen for the following differences between the two tracks:

1. the leading edges of the guitar plucks

2. the sibilance in his voice

 

One track is slightly softer (easier to listen to) in both cases... to my ears.

 

Mani.