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Random/OT: Low sample rate audio weirdness/mystery

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  Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-06 05:28 -0500
    Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-06 16:21 +0000
      Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-06 13:54 -0500
        Re: Random/OT: Low sample rate audio weirdness/mystery "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-09-06 13:18 -0700
          Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-06 15:42 -0500
            Re: Random/OT: Low sample rate audio weirdness/mystery "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-09-06 14:37 -0700
      Re: Random/OT: Low sample rate audio weirdness/mystery Terje Mathisen <terje.mathisen@tmsw.no> - 2025-09-07 12:26 +0200
        Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-07 14:59 -0500
          Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-07 21:13 +0000
            Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-07 18:58 -0500
              Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-07 21:16 -0500
                Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-07 22:55 -0500
                  Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-08 06:49 -0500
                    Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-08 23:28 -0500
                      Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-09 07:06 -0500
                        Re: Random/OT: Low sample rate audio weirdness/mystery Michael S <already5chosen@yahoo.com> - 2025-09-09 18:47 +0300
                          Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-09 20:27 -0500
        Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-07 21:12 +0000
          Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-08 10:59 +0200
            Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-08 15:10 -0500
              Re: Random/OT: Low sample rate audio weirdness/mystery scott@slp53.sl.home (Scott Lurndal) - 2025-09-08 21:10 +0000
                Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-08 18:57 -0500
                  Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-08 21:49 -0500
              Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-09 15:06 +0200
                Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-09 14:13 -0500
                  Re: Random/OT: Low sample rate audio weirdness/mystery scott@slp53.sl.home (Scott Lurndal) - 2025-09-09 20:55 +0000
                  Re: Random/OT: Low sample rate audio weirdness/mystery "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-09-09 14:15 -0700
                    Re: Random/OT: Low sample rate audio weirdness/mystery "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-09-09 14:17 -0700
                  Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-09 23:23 +0200
            Re: Random/OT: Low sample rate audio weirdness/mystery George Neuner <gneuner2@comcast.net> - 2025-09-08 17:57 -0400
              Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-08 23:51 +0000
              Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-09 15:51 +0200
                Re: Random/OT: Low sample rate audio weirdness/mystery George Neuner <gneuner2@comcast.net> - 2025-09-12 13:01 -0400
                  Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-12 12:23 -0500
                    Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-12 20:32 +0200
                      Re: Random/OT: Low sample rate audio weirdness/mystery George Neuner <gneuner2@comcast.net> - 2025-09-14 07:43 -0400
                        Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2025-09-14 15:08 +0200
                    Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-12 18:58 +0000
                      Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-12 14:30 -0500
                      Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-12 14:46 -0500
        Re: Random/OT: Low sample rate audio weirdness/mystery Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-22 03:18 -0800
      Re: Random/OT: Low sample rate audio weirdness/mystery Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-11 01:35 +0000
        Re: Random/OT: Low sample rate audio weirdness/mystery scott@slp53.sl.home (Scott Lurndal) - 2025-09-11 15:06 +0000
          Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2025-09-11 15:59 +0000
            Re: Random/OT: Low sample rate audio weirdness/mystery Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-19 02:10 +0000
          Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-11 12:56 -0500
    Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2025-09-06 11:59 -0500
      Re: Random/OT: Low sample rate audio weirdness/mystery "Brian G. Lucas" <bagel99@gmail.com> - 2025-09-06 12:31 -0500
    Re: Random/OT: Low sample rate audio weirdness/mystery Michael S <already5chosen@yahoo.com> - 2025-09-06 20:52 +0300
      Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-06 14:19 -0500
        Re: Random/OT: Low sample rate audio weirdness/mystery Lawrence D’Oliveiro <ldo@nz.invalid> - 2025-09-11 01:33 +0000
          Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2025-09-11 02:05 -0500
      Re: Random/OT: Low sample rate audio weirdness/mystery Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-01-22 03:31 -0800
        Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-01-22 15:21 -0600
          Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-01-23 00:13 +0000
            Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2026-01-22 18:36 -0600
              Re: Random/OT: Low sample rate audio weirdness/mystery MitchAlsup <user5857@newsgrouper.org.invalid> - 2026-01-23 02:00 +0000
                Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2026-01-22 20:20 -0600
                  Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-01-23 02:25 -0600
                    Re: Random/OT: Low sample rate audio weirdness/mystery Niklas Holsti <niklas.holsti@tidorum.invalid> - 2026-01-23 11:43 +0200
                      Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-01-23 05:27 -0600
                        Re: Random/OT: Low sample rate audio weirdness/mystery scott@slp53.sl.home (Scott Lurndal) - 2026-01-23 15:49 +0000
                      Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2026-01-23 17:37 +0100
                        Re: Random/OT: Low sample rate audio weirdness/mystery Niklas Holsti <niklas.holsti@tidorum.invalid> - 2026-01-23 18:56 +0200
                          Re: Random/OT: Low sample rate audio weirdness/mystery David Brown <david.brown@hesbynett.no> - 2026-01-23 18:14 +0100
                      Re: Random/OT: Low sample rate audio weirdness/mystery Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-14 20:44 -0800
                        Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-02-15 02:11 -0600
                    Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2026-01-23 11:07 -0600
                      Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-01-23 14:52 -0600
                Re: Random/OT: Low sample rate audio weirdness/mystery scott@slp53.sl.home (Scott Lurndal) - 2026-01-23 15:36 +0000
                Re: Random/OT: Low sample rate audio weirdness/mystery Andy Valencia <vandys@vsta.org> - 2026-01-23 15:35 -0800
              Re: Random/OT: Low sample rate audio weirdness/mystery Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-02-14 20:57 -0800
                Re: Random/OT: Low sample rate audio weirdness/mystery David Schultz <david.schultz@earthlink.net> - 2026-02-15 09:09 -0600
                  Re: Random/OT: Low sample rate audio weirdness/mystery Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-03-18 00:40 -0700
            Re: Random/OT: Low sample rate audio weirdness/mystery "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-01-22 17:04 -0800
              Re: Random/OT: Low sample rate audio weirdness/mystery BGB <cr88192@gmail.com> - 2026-01-23 05:13 -0600

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#114749

Terje Mathisen <terje.mathisen@tmsw.no> writes:

> MitchAlsup wrote:
>
>> BGB <cr88192@gmail.com> posted:
>>
>>> Just randomly thinking again about some things I noticed with audio at
>>> low sample rates.
>>>
>>> For baseline, can note, basic sample rates:
>>>     44100:  Standard, sounds good, but bulky
>>
>> No it does not sound "good" on a system that accurately reproduces
>> 22KHz; like systems with electrostatic speakers covering the high
>> end of the audio spectrum.
>>
>> Might sound "good" to someone who does not know what it is supposed
>> to actually sound like, though.
>
> My ears are not good enough to notice the difference between CD
> quality, AAC/high sample rate MP3/ogg vorbis/etc, but according to my
> savant (?) cousin who could listen to a 16 min piece of music once and
> then write down the score for all the instruments, none of them sound
> like live, but they are close enough that he can listen and internally
> translate to what it would have sounded like in a concert.

Anyone with ordinary hearing can tell the difference between
CD-quality audio and a high-quality analog audio path.  Like
what Mitch says, it's all about the phase relationships of
high frequencies.  Most people have just never had the
opportunity to listen to high-quality audio (especially
including speakers, but sometimes also other components),
and that fools them into thinking substandard digital
audio (especially CDs, but also others) is okay.  To do
a meaningful test needs better equipment than most people
have listened to.

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#113413

On Sat, 06 Sep 2025 16:21:12 GMT, MitchAlsup wrote:

> No it does not sound "good" on a system that accurately reproduces
> 22KHz; like systems with electrostatic speakers covering the high end of
> the audio spectrum.

I wonder how that works, given that the audio engineer that mastered the 
recording was using speakers that cost a fraction of the price.

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#113415

Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> writes:
>On Sat, 06 Sep 2025 16:21:12 GMT, MitchAlsup wrote:
>
>> No it does not sound "good" on a system that accurately reproduces
>> 22KHz; like systems with electrostatic speakers covering the high end of
>> the audio spectrum.
>
>I wonder how that works, given that the audio engineer that mastered the 
>recording was using speakers that cost a fraction of the price.

Have you priced quality studio monitors?   Obviously not.

A nice pair of intro electrostatics run about a USD1200 (magnapan lrs+).

A single studio monitor can easily cost more than USD12000.

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#113418

scott@slp53.sl.home (Scott Lurndal) posted:

> Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> writes:
> >On Sat, 06 Sep 2025 16:21:12 GMT, MitchAlsup wrote:
> >
> >> No it does not sound "good" on a system that accurately reproduces
> >> 22KHz; like systems with electrostatic speakers covering the high end of
> >> the audio spectrum.
> >
> >I wonder how that works, given that the audio engineer that mastered the 
> >recording was using speakers that cost a fraction of the price.
> 
> Have you priced quality studio monitors?   Obviously not.
> 
> A nice pair of intro electrostatics run about a USD1200 (magnapan lrs+).

Magnepan's are not electrostatic, but use the moving Mylar plane sort-of
like they were electrostatic--but they use magnetic strips on the backplane
to impart forces onto the Mylar plane.

Martin Logan speakers are electrostatic (I have a pair from 1986-ish, 
reved up from B-to-G in 1996.) They sound much like electrostatic
headphones except rooms sized sound pressure levels. These cost 
around $2,000 in 1986...

Dalhquist are electrostatic; around since 1973-ish.
 
> A single studio monitor can easily cost more than USD12000.

And often accompanied by a tuning system to allow the speakers to be tuned 
to the room in which they are used. Velodyne sub-woofers allow the woofer
to be tuned to the room and phase aligned with the main speakers.

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#113503

On Thu, 11 Sep 2025 15:59:32 GMT, MitchAlsup wrote:

>> A single studio monitor can easily cost more than USD12000.
> 
> And often accompanied by a tuning system to allow the speakers to be
> tuned to the room in which they are used.

For a long time, the “classic” pro studio monitor was the Yamaha NS-10, 
which I don’t think was ever anywhere in the “audiophile” price range.

Nor did it need tuning for the room: it was designed for nearfield use.

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#113421

On 9/11/2025 10:06 AM, Scott Lurndal wrote:
> Lawrence =?iso-8859-13?q?D=FFOliveiro?= <ldo@nz.invalid> writes:
>> On Sat, 06 Sep 2025 16:21:12 GMT, MitchAlsup wrote:
>>
>>> No it does not sound "good" on a system that accurately reproduces
>>> 22KHz; like systems with electrostatic speakers covering the high end of
>>> the audio spectrum.
>>
>> I wonder how that works, given that the audio engineer that mastered the
>> recording was using speakers that cost a fraction of the price.
> 
> Have you priced quality studio monitors?   Obviously not.
> 
> A nice pair of intro electrostatics run about a USD1200 (magnapan lrs+).
> 
> A single studio monitor can easily cost more than USD12000.
> 

I guess, this is a fair bit different, say, from using some $35 
headphones, or $60 for some external speakers, probably throwing some 
money Logitech's way...

Or, slightly cheaper, some "Amazon Basics" equivalents.
Or, more expensive, throwing their money at Bosch or Senheiser or similar.


Granted, there are cheaper headphones, but they are often lacking in 
terms of comfort and/or audio quality.


Otherwise, I would think an option would be to try to guess which sort 
of hardware consumers are most likely to be using, and then tune for 
best results on this (so, say, aim for cheap, but not too cheap).

...

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#113371

On 9/6/25 5:28 AM, BGB wrote:
>     8000: Very poor, speech almost unintelligible (normally).
>       But, it is seeming like a "weird hack" may exist here.

You might want to look at how AT&T did it. It has been a while but I 
think this is near what they used. Back when phones were analog and 
digital was just getting started.

-- 
http://davesrocketworks.com
David Schultz
"The cheaper the crook, the gaudier the patter." - Sam Spade

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#113372

On 9/6/25 11:59 AM, David Schultz wrote:
> On 9/6/25 5:28 AM, BGB wrote:
>>     8000: Very poor, speech almost unintelligible (normally).
>>       But, it is seeming like a "weird hack" may exist here.
> 
> You might want to look at how AT&T did it. It has been a while but I think this 
> is near what they used. Back when phones were analog and digital was just 
> getting started.
> 
That was T1 carrier.  When I looked at the schematics, I was surprised to see
the audio compression was done in analog, using the exponential curve of a
diode to get logarithmic compression.  If I remember correctly:-)

Brian

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#113374

On Sat, 6 Sep 2025 05:28:16 -0500
BGB <cr88192@gmail.com> wrote:

> Just randomly thinking again about some things I noticed with audio
> at low sample rates.
> 
> For baseline, can note, basic sample rates:
>    44100: Standard, sounds good, but bulky
>    32000: Sounds good
>    22050: Moderate
>    16000: OK, Modest size, acceptable quality.
>      Seems like best tradeoff if not going for high quality.
>    11025: Poor, muffled.
>     8000: Very poor, speech almost unintelligible (normally).
>       But, it is seeming like a "weird hack" may exist here.
>

8000 x 8bit (mu-law in USA, A-law in majority of the world) was a
standard sampling rate for digital back ends of analog wired telephony
for more than 50 years. I didn't check, but would assume that it still
is. 
Most people founded it quite intelligible. Certainly more intelligible
than cellular telephony, until less then 20 years ago cellular improved
a little.

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#113376

On 9/6/2025 12:52 PM, Michael S wrote:
> On Sat, 6 Sep 2025 05:28:16 -0500
> BGB <cr88192@gmail.com> wrote:
> 
>> Just randomly thinking again about some things I noticed with audio
>> at low sample rates.
>>
>> For baseline, can note, basic sample rates:
>>     44100: Standard, sounds good, but bulky
>>     32000: Sounds good
>>     22050: Moderate
>>     16000: OK, Modest size, acceptable quality.
>>       Seems like best tradeoff if not going for high quality.
>>     11025: Poor, muffled.
>>      8000: Very poor, speech almost unintelligible (normally).
>>        But, it is seeming like a "weird hack" may exist here.
>>
> 
> 8000 x 8bit (mu-law in USA, A-law in majority of the world) was a
> standard sampling rate for digital back ends of analog wired telephony
> for more than 50 years. I didn't check, but would assume that it still
> is.

It seems that the issue isn't (purely) with the sample rate or encoding.


But, there is some "weird hacks" that can be done in audio processing 
when downsampling that seems to notably increase intelligibility at an 
8kHz sample rate (in which case, A-Law is back to being effective again).


In general, I don't fault mu-law or A-Law as the quality they give is by 
far superior to 8-bit linear PCM.


Just, the "standard" audio down-sampling strategies (glorified averaging 
in various forms) just sort of result in audio becoming muffled and 
speech poorly intelligible at low sample rates.

Whereas, the "hacky" strategies (line or curve fitting) seem to give a 
better result.

I am more just sort of at a loss as to what is going on here exactly, as 
it appears to defy common wisdom about how audio resampling (or audio 
quality) should work.


Well, and as noted my perception is often at odds with what an RMSE 
score says (where RMSE tends to more strongly prefer the 
muffled-sounding versions). Where, usually, RMSE is sort of the gold 
standard of measuring quality in image and audio processing.


> Most people founded it quite intelligible. Certainly more intelligible
> than cellular telephony, until less then 20 years ago cellular improved
> a little.
> 

Whatever the cellphones are doing now, still sounds like garbage even 
versus what I get from 2-bit IMA ADPCM at 8kHz ...

Like, if I encode some speech as 2-bit ADPCM, at least I can still 
understand what is being said (even if 2-bit ADPCM doesn't necessarily 
give the best audio quality; and is kinda poorly supported in SW vs the 
more common 4-bit ADPCM).


Like, it is a disincentive to talk over the phone when I have to make 
extra effort to try to decipher what people are saying due to poor audio 
quality.


> 

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#113412

On Sat, 6 Sep 2025 14:19:40 -0500, BGB wrote:

> But, there is some "weird hacks" that can be done in audio processing 
> when downsampling that seems to notably increase intelligibility at an 
> 8kHz sample rate ...

There are digital encoding formats used with mobile phones that are 
optimized for speech. Ever heard a call where the other end sounded every 
now and then like they were underwater? That’s the kind of compression 
artifact you get.

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#113414

On 9/10/2025 8:33 PM, Lawrence D’Oliveiro wrote:
> On Sat, 6 Sep 2025 14:19:40 -0500, BGB wrote:
> 
>> But, there is some "weird hacks" that can be done in audio processing
>> when downsampling that seems to notably increase intelligibility at an
>> 8kHz sample rate ...
> 
> There are digital encoding formats used with mobile phones that are
> optimized for speech. Ever heard a call where the other end sounded every
> now and then like they were underwater? That’s the kind of compression
> artifact you get.

Looking some at it, apparently a lot of the current modern phone class 
audio codecs are based on trying to run a model of the human vocal tract 
and then adding white noise to make it sound more natural (with some 
apparently partly based on vocoder technology).

But, in my case, I don't really hear speech effectively over phones, I 
mostly hear a lot of warbling that I am left trying to decipher over all 
the hiss.


As noted, the filtering hack mostly kept to normal PCM handling, but I 
soon realized can't work as a general solution to "stuff sounding bad" 
at an 8kHz sample rate.



When I was looking into it, 4-channel sinewave synthesis is possible, but:
Quality is still poor;
At a 125Hz update frequency, at 16 bits per sinewave, still takes around 
8kbps.

Needs 16 bits roughly to encode both the frequency and amplitude of each 
sinewave to an acceptable degree.

When fiddling with it, I ended up finding an OK strategy of:
Sample for 12 signwaves, dividing the 2-8 kHz range into roughly 1/6 
octave chunks (picking the loudest wave within each chunk);
Pick the top 4 loudest waves from the 12 sampled.


I was experimenting with pushing the scheme I mentioned else-thread to 
around 6 kbps, which (last I messed with it) still generates some truly 
awful audio quality.

Posted an example to my twitter feed:
https://x.com/cr88192/status/1965694742186049683

It does sound a fair bit better with a 16kHz sampling rate (12kbs), but 
is still notably inferior to 8kHz 2-bit ADPCM (16kbps).


The 6kbps case is interesting as it gets a 2-minute song into around 
96K, which is kinda pushing into MIDI territory. But, MIDI would have 
sounded better (though, no real obvious way to auto-convert PCM audio 
into MIDI commands).

Well, unless maybe doing something like sinewave synthesis but then 
trying to convert the sine waves into Note On/Off commands. Though, 
naively mapping sinewave synthesis to MIDI commands would likely add a 
fair bit of bulk and overhead.



It is possible that I may need to take a different approach to 
generating the pattern table.

Initial approach:
   Fill it with sine-waves;
     Didn't work very well.
   Current strategy:
     Start with a table of 16-bit patterns (curated manually);
     Map each to samples, 0=full negative, 1=full positive;
     Run N passes of averaging;
     Generate a pattern table with 4-bits per pattern sample.

Possible pattern-table generation strategy (not yet tried):
Use the sign of each sample relative to the base curve to generate a 
16-bit key;
average the relative values for each key, keeping track of relative 
usage frequency;
Pick the top-N else merge similar patterns until one has fewer than 256 
or so.

Note that any sounds much over ~ 250Hz at an 8000 sample rate are being 
generated from the pattern table.


But, it is possible this approach may be a lost cause (could not be made 
to give anywhere acceptable quality at these bitrates).


Note that I don't want something significantly more complicated or 
expensive than ADPCM (so, ideally no entropy coding or fancy transforms 
on the decoder side...).

To be useful, would need to either:
   Do better than ADPCM at a similar bitrate;
   Achieve bitrates lower than what is possible with ADPCM.

Was partly looking at the latter, but to be useful it needs to have some 
level of "passable" quality, which I have yet to achieve at this target 
(eg, particularly at 6 kbps).

...

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#114750

Michael S <already5chosen@yahoo.com> writes:

> On Sat, 6 Sep 2025 05:28:16 -0500
> BGB <cr88192@gmail.com> wrote:
>
>> Just randomly thinking again about some things I noticed with audio
>> at low sample rates.
>>
>> For baseline, can note, basic sample rates:
>>    44100:  Standard, sounds good, but bulky
>>    32000:  Sounds good
>>    22050:  Moderate
>>    16000:  OK, Modest size, acceptable quality.
>>      Seems like best tradeoff if not going for high quality.
>>    11025:  Poor, muffled.
>>     8000:  Very poor, speech almost unintelligible (normally).
>>       But, it is seeming like a "weird hack" may exist here.
>
> 8000 x 8bit (mu-law in USA, A-law in majority of the world) was a
> standard sampling rate for digital back ends of analog wired telephony
> for more than 50 years.  I didn't check, but would assume that it still
> is.
> Most people founded it quite intelligible.

Yes but bit rate isn't the whole story.  First the measure is not
"good sound" but only "understandable sound".  Second telephony
does frequency filtering in a very different way than digital
audio does.  Voices on phones are recognizable but still easily
differentiable from the original.  Music played via phone-quality
audio sounds terrible.

> Certainly more intelligible
> than cellular telephony, until less then 20 years ago cellular improved
> a little.

Cell phone audio...  even today, ick, double ick, and triple ick.

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#114754

On 1/22/2026 5:31 AM, Tim Rentsch wrote:
> Michael S <already5chosen@yahoo.com> writes:
> 
>> On Sat, 6 Sep 2025 05:28:16 -0500
>> BGB <cr88192@gmail.com> wrote:
>>
>>> Just randomly thinking again about some things I noticed with audio
>>> at low sample rates.
>>>
>>> For baseline, can note, basic sample rates:
>>>     44100:  Standard, sounds good, but bulky
>>>     32000:  Sounds good
>>>     22050:  Moderate
>>>     16000:  OK, Modest size, acceptable quality.
>>>       Seems like best tradeoff if not going for high quality.
>>>     11025:  Poor, muffled.
>>>      8000:  Very poor, speech almost unintelligible (normally).
>>>        But, it is seeming like a "weird hack" may exist here.
>>
>> 8000 x 8bit (mu-law in USA, A-law in majority of the world) was a
>> standard sampling rate for digital back ends of analog wired telephony
>> for more than 50 years.  I didn't check, but would assume that it still
>> is.
>> Most people founded it quite intelligible.
> 
> Yes but bit rate isn't the whole story.  First the measure is not
> "good sound" but only "understandable sound".  Second telephony
> does frequency filtering in a very different way than digital
> audio does.  Voices on phones are recognizable but still easily
> differentiable from the original.  Music played via phone-quality
> audio sounds terrible.
> 

In general, A-Law generates better sounding audio.

But, at low sample rates (eg, 8 kHz), I had noted that ADPCM gives more 
intelligible speech than A-Law, even if the A-Law "sounds nicer".

Like, if you want background music, 8kHz A-Law is OK.

But, to understand what anyone is saying, less ideal IME, as it tends to 
be more muffled than what I was getting with ADPCM. Contrast, ADPCM is 
different, in that while intelligibility is higher, it also has a more 
"gritty" sound (particularly in variants at 2-bits / sample).

Had also noted:
Low pass filtering reduces "grittiness" by also negatively effects 
intelligibility;
High pass filtering preserves intelligibility but can cause a more 
"tinny" sound (say, if one uses a 2kHz high-pass filter, so that the 
ADPCM only really encodes the 2kHz to 4kHz band).


In my past testing, seems like 2kHz to 4kHz is the most important band 
for speech intelligibility (at least for me). It is improved with the 
4kHz to 8kHz band, but it seems like this is less important.

So, ranking bands for relative importance:
   < 500 Hz : Mostly N/A (*)
  0.5- 1 kHz: 5th (barely noticable)
    1- 2 kHz: 3rd (makes sound "fuller")
    2- 4 kHz: 1st
    4- 8 kHz: 2nd
    8-16 kHz; 4th (small effect)
   16-32 kHz: Mostly unnoticable

*: Mostly inaudible as sine waves, but still very audible if some form 
of square wave. But, it would seem like I may be "mostly deaf" in this 
range (I can detect sounds here more through tactile senses than by 
hearing them via ears). This effect though more depends on touching a 
surface, and the relative properties of the object in question.


Subjective responses from house-cats do seem to imply that to them there 
is a more obvious difference between the original audio and high-pass or 
band-pass versions.

Like, play a normal version of a song, and they remain calm, but play a 
2kHz high-pass version and they dig in their claws and seem displeased 
(implying a more obvious difference in the sound of the audio than my 
own subjective experience).


>> Certainly more intelligible
>> than cellular telephony, until less then 20 years ago cellular improved
>> a little.
> 
> Cell phone audio...  even today, ick, double ick, and triple ick.


Cell phone audio:
Pretty much unintelligible.

Mostly warbling noises and hiss...

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#114755

BGB <cr88192@gmail.com> posted:

> On 1/22/2026 5:31 AM, Tim Rentsch wrote:
> > Michael S <already5chosen@yahoo.com> writes:
> > 
> >> On Sat, 6 Sep 2025 05:28:16 -0500
> >> BGB <cr88192@gmail.com> wrote:
> >>
> >>> Just randomly thinking again about some things I noticed with audio
> >>> at low sample rates.
> >>>
> >>> For baseline, can note, basic sample rates:
> >>>     44100:  Standard, sounds good, but bulky
> >>>     32000:  Sounds good
> >>>     22050:  Moderate
> >>>     16000:  OK, Modest size, acceptable quality.
> >>>       Seems like best tradeoff if not going for high quality.
> >>>     11025:  Poor, muffled.
> >>>      8000:  Very poor, speech almost unintelligible (normally).
> >>>        But, it is seeming like a "weird hack" may exist here.
> >>
> >> 8000 x 8bit (mu-law in USA, A-law in majority of the world) was a
> >> standard sampling rate for digital back ends of analog wired telephony
> >> for more than 50 years.  I didn't check, but would assume that it still
> >> is.
> >> Most people founded it quite intelligible.
> > 
> > Yes but bit rate isn't the whole story.  First the measure is not
> > "good sound" but only "understandable sound".  Second telephony
> > does frequency filtering in a very different way than digital
> > audio does.  Voices on phones are recognizable but still easily
> > differentiable from the original.  Music played via phone-quality
> > audio sounds terrible.
> > 
> 
> In general, A-Law generates better sounding audio.
> 
> But, at low sample rates (eg, 8 kHz), I had noted that ADPCM gives more 
> intelligible speech than A-Law, even if the A-Law "sounds nicer".

I am not listening for the sound to be good or bad, I am listening
whether {the violin sounds like a violin, the trumpet sounds like a
trumpet, and the drums sound like drums} when listening to them live!

That is what was the hallmark of "Hi Fi" when I started (1965-ish.)
-----------------------
> 
> In my past testing, seems like 2kHz to 4kHz is the most important band 
> for speech intelligibility (at least for me). It is improved with the 
> 4kHz to 8kHz band, but it seems like this is less important.

The timber of instruments requires phase accurate reproduction of
frequencies up to at least 15KHz.

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#114756

On 1/22/26 6:13 PM, MitchAlsup wrote:
> The timber of instruments requires phase accurate reproduction of
> frequencies up to at least 15KHz.

Define "phase accurate". As in how much phase error at say 20KHz is 
acceptable to you. 1 degree? 10?

And how do you maintain that through the signal chain? In, for example, 
speaker crossover networks.


Instead of chasing performance at frequencies I am increasingly less 
able to hear, I went the other way. A subwoofer so that pipe organs, and 
other things that reach down to 20Hz, sound impressive.


-- 
http://davesrocketworks.com
David Schultz
"Gag me with a Smurf"

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#114758

David Schultz <david.schultz@earthlink.net> posted:

> On 1/22/26 6:13 PM, MitchAlsup wrote:
> > The timber of instruments requires phase accurate reproduction of
> > frequencies up to at least 15KHz.
> 
> Define "phase accurate". As in how much phase error at say 20KHz is 
> acceptable to you. 1 degree? 10?

When instruments quit sounding like they sound in person.
 
> And how do you maintain that through the signal chain? In, for example, 
> speaker crossover networks.

I use a full range electrostatic speaker (Martin Logan CLS (Rev G))
 
> 
> Instead of chasing performance at frequencies I am increasingly less 
> able to hear, I went the other way. A subwoofer so that pipe organs, and 
> other things that reach down to 20Hz, sound impressive.

Velodyne DD15 SubWoofer (and then spent couple hours tuning its
8 stage variable frequency crossover so that 15Hz to 5KHz was as 
flat as possible.) Sub mainly carries 15Hz-65Hz.

Also note:: Room is 17 feet wide and 57 feet long, you can play as 
low as about 1 Watt and hear everything while others are carrying
on conversations.

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#114759

On 1/22/26 8:00 PM, MitchAlsup wrote:
> 
> David Schultz <david.schultz@earthlink.net> posted:
>> Define "phase accurate". As in how much phase error at say 20KHz is
>> acceptable to you. 1 degree? 10?
> 
> When instruments quit sounding like they sound in person.

Hardly an objective standard and you can't design to it.

>   
>> And how do you maintain that through the signal chain? In, for example,
>> speaker crossover networks.
> 
> I use a full range electrostatic speaker (Martin Logan CLS (Rev G))
>   
A rare and specialized speaker. What about the rest of us?

And what about the phase errors resulting from varying distances from 
different parts of the panel to your ears?


> Velodyne DD15 SubWoofer (and then spent couple hours tuning its
> 8 stage variable frequency crossover so that 15Hz to 5KHz was as
> flat as possible.) Sub mainly carries 15Hz-65Hz.

I use a Velodyne SMS1 with my home built sub. (JBL2245H driver) Strange 
thing, the brick SMPS failed. Resulting in hum from the sub. Easy to 
replace but just added to my dislike of SMPS in general. I good idea but 
rarely executed well. The damn things keep failing after far too short a 
time.



-- 
http://davesrocketworks.com
David Schultz
"Gag me with a Smurf"

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#114760

On 1/22/2026 8:20 PM, David Schultz wrote:
> On 1/22/26 8:00 PM, MitchAlsup wrote:
>>
>> David Schultz <david.schultz@earthlink.net> posted:
>>> Define "phase accurate". As in how much phase error at say 20KHz is
>>> acceptable to you. 1 degree? 10?
>>
>> When instruments quit sounding like they sound in person.
> 
> Hardly an objective standard and you can't design to it.
> 
>>> And how do you maintain that through the signal chain? In, for example,
>>> speaker crossover networks.
>>
>> I use a full range electrostatic speaker (Martin Logan CLS (Rev G))
> A rare and specialized speaker. What about the rest of us?
> 
> And what about the phase errors resulting from varying distances from 
> different parts of the panel to your ears?
> 

I am currently using some ~ $35 Logitech gaming headphones.

Previously I had gotten some cheaper $15 headphones to replace some of 
my old headphones (also Logitech) which had gotten so old they were 
falling apart. The cheaper headphones sounded kinda like muffled 
dog-crap though, so ended up spending the "big money" on some headphones 
that "probably wont sound like crap".

Ironically, ended up giving them to my dad who is hard of hearing, 
apparently he also noticed that they sounded like muffled crap though.

Granted, more expensive headphones exist, but I am not made of money.



> 
>> Velodyne DD15 SubWoofer (and then spent couple hours tuning its
>> 8 stage variable frequency crossover so that 15Hz to 5KHz was as
>> flat as possible.) Sub mainly carries 15Hz-65Hz.
> 
> I use a Velodyne SMS1 with my home built sub. (JBL2245H driver) Strange 
> thing, the brick SMPS failed. Resulting in hum from the sub. Easy to 
> replace but just added to my dislike of SMPS in general. I good idea but 
> rarely executed well. The damn things keep failing after far too short a 
> time.
> 

Not used much in terms of dedicated speakers in a long time, but 
generally I don't want to be making noise that other people would hear.


> 
> 

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#114761

On 2026-01-23 10:25, BGB wrote:

    [snip]

> I am currently using some ~ $35 Logitech gaming headphones.

    [snip]

> Granted, more expensive headphones exist, but I am not made of money.

Indeed. I had occasion recently to inquire about headphones at a large 
local electronics shop. The assistant asked for my price range, and when 
I hesitated, he mentioned that their range went up to 65 kilo-euro. Talk 
about "framing" a price discussion :-)

The shop had one of those items in a locked glass display case. 
Reportedly each pair of headphones is hand-built. They come with a white 
veined marble stand that is also an electronics box, with eight or ten 
vacuum tubes mounted visibly on the top surface. The builder comes to 
your home to personally install and tune the stuff for your environment. 
The price, however, was only 62 999 euro; perhaps it was discounted as a 
display item.

We settled on a cheaper model.

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