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  • 2Bdecided
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Audibility of 20kHz brick wall filtering
This test continues the discussion in this thread...

http://www.hydrogenaudio.org/forums/index....67619&st=75

...using the impulses provided at the end of that thread as filters.



I've filtered some 24/96 audio with the linear phase (050) and maximum phase (100) 20k impulses, and uploaded the results here:

http://rapidshare.de/files/41301790/limehouse_20k.zip.html

The "reference" is just the original convolved with an impulse, i.e. a null operation.

All files are 24-bit 96kHz sampled .wav files. You will need a 24/96 sound card to listen to these files, and use something like foobar2k which plays the files properly.

The "reference" should sound best, the "maximum phase" file should sound worst. Can anyone ABX a difference?

(I don't claim to be able to hear any difference).


btw, the files are time aligned to the nearest sample, though the maximum phase filter introduces a sub-sample delay and slight phase shift. I've confirmed that all low pass filters have identical amplitude responses, and that the pass band of the low pass filters matches the level of the unit impulse. Source: Cool Edit Pro frequency analysis, 65536 FFT, Linear View, Range 24 dB, Reference -90 dBFS, window expanded to fill my screen, absolutely no different between plots.

In the last second end of each audio file is a unit impulse, filtered - hence the filter itself is "included" in the file, for easy checking, analysis and verification.


(I used Cool Edit Pro to do the convolution (filtering). I'm not entirely convinced by its algorithm - there are some errors 100dB below the signal, verified by convolving with a single impulse. From the nature of the errors, I assume it's performing time domain convolution by frequency domain multiplication, which is quite common, and there are some rounding errors which would be lost in the noise of a 16-bit signal, but are apparent with the 24-bit signal)

Cheers,
David.

P.S. When I tried to FLAC encode these files (using FLAC 1.2.1b in Windows XP), the FLAC verifier from the same package (not the one called automatically when encoding, but the stand-alone one) reported errors, hence I've provided .wavs instead. I hope my system isn't on the way out - can anyone else reproduce this problem?

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #1
btw, the maximum phase file should sound worst.

I can't hear any difference.

Cheers,
David.

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #2
I guess this is quite a challenge then?

Cheers,
David.

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #3
I've attached some spectral plots to show how significant the ringing is at 20kHz.

limehouse1.jpg shows the original (top) and filtered (bottom).

The broad shaded vertical lines are drum hits, the little horizontal flecks at the top left of them in the bottom image are the pre-ringing of the maximum phase filter.

The vertical dotted line represents the cursor. limehouse2.jpg shows the spectrum at the cursor. You can see the spike at 20kHz. It's about 10dB less than the energy in the drum hit itself (not shown).

Cheers,
David.

  • Axon
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Audibility of 20kHz brick wall filtering
Reply #4
I, probably like most people here, can't hear a whit above 18k to begin with. So I'm not even going to try.

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #5
I, probably like most people here, can't hear a whit above 18k to begin with. So I'm not even going to try.
According to people who believe in such things, that shouldn't disqualify you at all...

Quote
The preference for higher sample rates is not based on ultrasonic content, but on time resolution and aliasing when conversion goes wrong. All anti-alias filters are brick wall, anti-causal (i.e. pre-ring) which is unnatural. You can hear the difference between different sample rates, even when the tweeter doesn't go above 18kHz and/or your hearing stops at 17kHz.
from here:
http://www.hydrogenaudio.org/forums/index....st&p=609606

Cheers,
David.
  • Last Edit: 16 January, 2009, 06:16:24 AM by 2Bdecided

  • MLXXX
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Audibility of 20kHz brick wall filtering
Reply #6
David,
I tried the reference against the maximum phase version.  I decided on just 5 trials, as I find ABX listening quite a strain, but 5 trials gives a fairly convincing outcome if all answers are correct.  I find a segment of about 1 or two seconds' duration that seems to sound different.  I then try to avoid answering until I am quite sure of the answer.

Results were as follows:

[blockquote]foo_abx 1.3.3 report
foobar2000 v0.9.6
2009/01/27 19:56:49

File A: C:\Users\Public\Downloads\ha\limehouse_20k\limehouse_maximum_phase_100.wav
File B: C:\Users\Public\Downloads\ha\limehouse_20k\limehouse_reference.wav

19:56:49 : Test started.
19:59:06 : 01/01  50.0%
19:59:33 : 02/02  25.0%
20:00:29 : 03/03  12.5%
20:15:11 : 04/04  6.3%
20:16:43 : 05/05  3.1%
20:16:48 : Test finished.

----------
Total: 5/5 (3.1%)
[/blockquote]
The 'maximum phase shifted version' sounded a bit duller to my ears.

I took a long refresh break for trials 4 and 5 because my hearing had temporarily lost its ability to discriminate fine differences.  Also the segment I chose to listen to for trials 4 and 5 was different from the segment I used for trials 1, 2 and 3.

I do not have particularly good high frequency hearing.  These days it cuts out before 20KHz.

It is of course always possible that something in my playback equipment created the difference.  There are always some lingering doubts about results like these.

Cheers


  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #7
Thank you MLXXX. It's great to see someone take the time and effort to do this.


Yes, it could be something in the playback equipment, but we wouldn't get useful ABX results without any playback equipment.

What playback equipment did you use?

Cheers,
David.

  • MLXXX
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Audibility of 20kHz brick wall filtering
Reply #8
Hopefully some others can do an ABX and report their results!

My playback system is a home theatre pc with an onboard high definition sound chip outputting discrete analogue channels.  The analogue channels are connected to an AVR, driving medium quality hi-fi speakers.

Some details that may possibly be relevant:
  • Foobar
  • Vista Home Premium operating platform
  • 2.4GHz core 2 duo processor in an Intel DG965WH motherboard
  • Default Vista high definition audio driver (Microsoft 21/6/2006 6.0.6000.1636)
  • Analogue connections from motherboard onboard high definition audio to Yamaha AVR (model HTR-5750). Tone controls defeated.
  • Magnat Vintage 350 main speakers
  • Listening volume: comfortable, not particularly loud
  • Listening distance: 3 metres
[/size]

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #9
The files I linked to in this thread have expired.

I've re-uploaded them here:

www.media fire.com/?sharekey=605ee2b5f85656f5e62ea590dc5e5dbb4b15895e9b73e977e91dc00c2f906379

You'll need to copy+paste the URL, and remove the space between media and fire, to make it work.

Cheers,
David.

Audibility of 20kHz brick wall filtering
Reply #10
The files I linked to in this thread have expired.
To make sure the files remain accessible, I've also put them online on my website.
Note that these are slightly modified files made on Jul 9 2010 by bandpass.
The shell-script used to generate the latest samples is available as well.

phases.zip
phases-20k.zip
phases-gen (shell-script)
limehouse_20k.zip
ringing.zip

Enjoy
Kees
  • Last Edit: 10 July, 2010, 03:05:21 PM by greynol

  • Cavaille
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Audibility of 20kHz brick wall filtering
Reply #11
Ugh, I don´t like ABX... always stressing. Took me roughly 7 minutes and now I´m having a slight headache. I always get headaches...

Well, here it is anyway:

Quote
foo_abx 1.3.4 report
foobar2000 v1.0.3
2010/07/10 03:21:48

File A: C:\Users\Eunice\Desktop\Limehouse\limehouse_reference.wav
File B: C:\Users\Eunice\Desktop\Limehouse\limehouse_maximum_phase_100.wav

03:21:48 : Test started.
03:22:36 : 01/01  50.0%
03:23:58 : 02/02  25.0%
03:25:05 : 03/03  12.5%
03:25:27 : 04/04  6.3%
03:26:12 : 05/05  3.1%
03:27:15 : 06/06  1.6%
03:28:16 : 07/07  0.8%
03:28:18 : Test finished.

----------
Total: 7/7 (0.8%)


The maximum phase version sounds not so pristine, transients seemed to have less "bite" (the clapping for instance). And I thought that the room response changed. I always write a sentence like this one: the room holding the microphones together vanishes. Well, sort of.

Independently from each other I thought that both versions sounded very good. What a marvelously engineered recording!

Oh, my system:
Quote
Windows 7 64
Pentium E6300, ASUS P5Q SE Plus
foobar2000 with Kernel Streaming
ASUS Xonar Essence ST
Sennheiser HD-600
  • Last Edit: 09 July, 2010, 09:46:46 PM by Cavaille
marlene-d.blogspot.com

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #12
That's two independent positive ABX results - now this is getting interesting!


Independently from each other I thought that both versions sounded very good. What a marvelously engineered recording!
It certainly sounds like you're in the room - though I'm not 100% happy with the sound that's in the room.

I think this recording is astonishing...
http://www.soundkeeperrecordings.com/format.htm
...though I don't believe it's as suitable for revealing the potential effects of a 20k LPF so well. I could be completely wrong of course! I'll have a play next week if I remember.

Cheers,
David.
  • Last Edit: 10 July, 2010, 05:27:57 AM by 2Bdecided

  • mzil
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Audibility of 20kHz brick wall filtering
Reply #13
Unless it is on my end, the rapidshare download page won't load.
I only gave it a go, not thinking I'll have any luck at differentiating the filters, only because I was curious what the music and or signal would be and there was an invitation to give it a go in another thread today.

If it's a hassle to reinstate the files, don't bother on my behalf.  It's not a biggie, I just thought I'd point it out.

Audibility of 20kHz brick wall filtering
Reply #14
Unless it is on my end, the rapidshare download page won't load.
Please check post #11. These links should still work.

  • 2Bdecided
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Audibility of 20kHz brick wall filtering
Reply #15
Another ABX report of these samples can be found here:
http://www.hydrogenaud.io/forums/index.php...st&p=880594

  • bandpass
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Audibility of 20kHz brick wall filtering
Reply #16
As discussed in another thread it seems that foo_abx has a flaw that makes it unsuitable for this sort of test: e.g. starting the playback where the cursor is in the spectrogram a few posts above constitutes a truncation which causes the 20kHz energy at that point to spread over the entire audible spectrum.

Audibility of 20kHz brick wall filtering
Reply #17
As discussed in another thread it seems that foo_abx has a flaw that makes it unsuitable for this sort of test: e.g. starting the playback where the cursor is in the spectrogram a few posts above constitutes a truncation which causes the 20kHz energy at that point to spread over the entire audible spectrum.



Please state in a more comprehensible fashion.

  • xnor
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Audibility of 20kHz brick wall filtering
Reply #18
Yeah please post this here in a more detailed fashion.
"I hear it when I see it."

  • bandpass
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Audibility of 20kHz brick wall filtering
Reply #19
Yeah please post this here in a more detailed fashion.

Done.

  • Wombat
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Audibility of 20kHz brick wall filtering
Reply #20
foo_abx 2.0 beta 4 report
foobar2000 v1.3.4
2014-11-14 16:20:39

File A: limehouse_maximum_phase_100.wav
SHA1: 722dc26db8d4ce666dc03875b2c8d4570d22b521
File B: limehouse_reference.wav
SHA1: e8ad96830d23cad4bba5bf822ce875ae452b9e7c

Output:
DS : Primärer Soundtreiber

16:20:39 : Test started.
16:21:02 : 00/01
16:21:25 : 00/02
16:21:49 : 00/03
16:22:01 : 01/04 <--- Difference found (FFT started)
16:22:08 : 02/05
16:22:17 : 03/06
16:22:28 : 04/07
16:22:39 : 05/08
16:22:47 : 06/09
16:23:02 : 07/10
16:23:02 : Test finished.

----------
Total: 7/10
Probability that you were guessing: 17.2%

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