From Newsgroup: comp.arch

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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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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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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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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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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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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On Tue, 9 Sep 2025 15:51:10 +0200, David Brown
<david.brown@hesbynett.no> wrote:

On 08/09/2025 23:57, George Neuner wrote:

:

This means most notes will include sounds that are outside the range
of (normal) human hearing, but you can still /feel/ these sounds [even
the high ones] and miss them when they are absent.

Nope. Most notes are much lower, and harmonics of relevance are within
the range of human hearing. For high enough notes, you simply don't
hear as much harmonic information.

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

C8 (high C) on the piano is ~4186 Hz. Assuming the need for the 7th
higher harmonic - 29302 Hz - Nyquist would demand a minimum sampling
rate of 58604/s to accurately reproduce C8.

You can't accurately hear C8 even when live - you don't get the same >harmonic information as you do with C6, because your ears can't
distinguish the higher harmonics. Your ears have the same limitations
as any other senses in this manner - you can look at your cat's feet and >count its toes, but if you look at a fly's feet you can't count the toes.

My point was about sampling and reproduction, not whether the note
could be heard. There is not a lot of piano music that involves the
1st, 7th or 8th octaves - because the 1st octave is jarring and the
7th and 8th (in general) are too high to carry to the audience without amplification.

In practice, unless you like orchestral, or certain folk or country,
you are not likely to hear much difference between a CD and a decent
quality compressed version of it. But the CD itself is not a faithful
reproduction of the live performance.

Good quality compressed formats are often better than CD quality. The >killer for CD quality is not the sample rate, it is the limited dynamic >range from the linear 16-bit range. Compressed formats will, in effect,
use a more logarithmic scale (like A-law and mu-law, used to get >comprehensible speech despite a much smaller sample size) that is more
in line with the way the human brain interprets sound.

And, of course, if you like orchestral you are more likely to be
listening to vinyl rather than CD. 8-)

In theory (but very rarely in practice), when combined with good enough >amplifiers and speakers, vinyl has a a higher dynamic range than CD
audio. But that is only the case when the record is new. Play it a few >times, and the wear from the needle will smooth out the tracks enough to >eliminate the difference.

True, but in fact there are laser based record players that do not
touch or damage the media. You still need to worry about warping, so
it is necessary to store your records properly.

I don't deal much with vinyl records myself anymore, but my sister has
an extensive collection.

But enjoying music is a psychologically, physically, mentally and >biologically complex hobby. The comfort of the chair you are sitting
in, or the type of reflections and absorptions from the rest of the
room, can make a big difference. Knowing that you have spent a great
deal of money on your impressive-looking hifi system will improve your >listening experience regardless of what any audio measurement might say.
Some audiophiles prefer the "valve sound" over "transistor sound" -
not because the sound reproduction is more accurate (it is not - valves
add second harmonic distortion that is non-existent in transistor >amplifiers), but simply because they like it better.

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On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

One of the coolest things I ever heard, felt really, were the beat tones between a couple of peddle notes on the pipe organ at the Meyerson in
Dallas.
--
http://davesrocketworks.com
David Schultz
"The cheaper the crook, the gaudier the patter." - Sam Spade
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On 12/09/2025 19:23, David Schultz wrote:

On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

Harmonics are always integer multiples of the base frequency, not
fractions - that's the definition of a harmonic.

You can get lower frequencies produced as beats when different
instruments play nominally the same note, but are a little out of tune.
That's not something you would normally want to have in music (though it
is a very useful effect for getting things in tune).

One of the coolest things I ever heard, felt really, were the beat tones between a couple of peddle notes on the pipe organ at the Meyerson in Dallas.

Big pipe organs have notes that are too low for human hearing, but the
volume is enough to feel them. Infrasound (sound below the lowest
audible frequency) has long been associated with feelings of
"supernatural" or "paranormal", increasing stress and tension. Horror
movies sometimes like to have them in their soundtracks, and more than
one "haunted house" turned out to have issues with the plumbing,
ventilation or nearby diesel engines that produced infrasound that made
people feel uneasy without knowing why. I'd imagine that for a church
organ, playing some infrasound notes will help the listeners feel
"religious" or feel some kind of "spiritual presence", though I have not
heard of that being done intentionally except by some of the more
dedicated fake healer conmen.

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

On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

One of the coolest things I ever heard, felt really, were the beat tones between a couple of peddle notes on the pipe organ at the Meyerson in Dallas.

Have you listened to a helicopter-style sub-woofer ??

Generally housed between stories in a building--a helicopter arranged set
of blades, that can go all the way down to 0 Hz--and up to about 30 Hz.
The low frequency components adjust the pitch of the blades through the
cyclic.
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On 9/12/2025 1:58 PM, MitchAlsup wrote:

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

On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

One of the coolest things I ever heard, felt really, were the beat tones
between a couple of peddle notes on the pipe organ at the Meyerson in
Dallas.

Have you listened to a helicopter-style sub-woofer ??

Generally housed between stories in a building--a helicopter arranged set
of blades, that can go all the way down to 0 Hz--and up to about 30 Hz.
The low frequency components adjust the pitch of the blades through the cyclic.

Main subwoofers I am aware of/had seen:
Large plastic-cone speakers;
Seemingly, the relative rigidity of a plastic cone works well here.
Large solenoid driving a big/heavy weight (such as a big chunk of
steel), which is then bolted down to something (presumably, the surface
of whatever it is bolted to serving a similar role to the speaker cone).




well, in other news, have slightly improved the quality of my new
experimental audio compressor at 6 kbps, but it is still pretty bad.
Seems my previous attempt (that I had posted online) was suffering from
32-bit truncation in the pattern table (some stuff was happening with
'int' that should have been with 'unsigned long long'; which was
negatively effecting audio quality).

...


TODO: Might still be worth testing it out at 32kHz / 24kbps, and see how
it compares against low bitrate MP3. If it doesn't sound completely
awful, might be OK (only reason I think it may stand a chance is because
of how terrible MP3 sounds at these sorts of bitrates).

At 16kHz (and 12kbps), does sound a bit better, though audio quality is
still inferior at present to 8000 2-bit ADPCM (16kbps).

...


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On 9/12/25 1:58 PM, MitchAlsup wrote:

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

One of the coolest things I ever heard, felt really, were the beat tones
between a couple of peddle notes on the pipe organ at the Meyerson in
Dallas.

Have you listened to a helicopter-style sub-woofer ??

No. I built a sub a decade or three ago (JBL 2245H driver) but have
never wanted to go quite so far as to build a rotary subwoofer.


The 18" sub gets as freaky as I want it to.
--
http://davesrocketworks.com
David Schultz
"The cheaper the crook, the gaudier the patter." - Sam Spade
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On Fri, 12 Sep 2025 20:32:48 +0200, David Brown
<david.brown@hesbynett.no> wrote:

On 12/09/2025 19:23, David Schultz wrote:

On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below
the (average) hearing threshold.

Harmonics are always integer multiples of the base frequency, not
fractions - that's the definition of a harmonic.

I learned them as "overtones" ... but it seems that musicians call
them all "harmonics" regardless of whether they are higher or lower.

MMV.
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On 14/09/2025 13:43, George Neuner wrote:

On Fri, 12 Sep 2025 20:32:48 +0200, David Brown
<david.brown@hesbynett.no> wrote:

On 12/09/2025 19:23, David Schultz wrote:

On 9/12/25 12:01 PM, George Neuner wrote:

You are forgetting the lower harmonics. If it is true about 3 lower,
then ~1/3 of notes on the piano will include an overtone that is below >>>> the (average) hearing threshold.

Harmonics are always integer multiples of the base frequency, not
fractions - that's the definition of a harmonic.

I learned them as "overtones" ... but it seems that musicians call
them all "harmonics" regardless of whether they are higher or lower.

MMV.

I'm not a musician - my knowledge of harmonics is from maths, physics,
signal processing, motor control, and that kind of thing. Maybe
musicians use the term slightly differently.

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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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