The $10000 Hi-Fi

On 5/5/2015 9:52 PM, Cedron wrote:
> [...snip...]
>
>> I don't remember
>> the exact context, but I do remember the change: the switched to rounding
> at
>> the 24th bit to truncating at the 24th bit. Conventional wisdom said
> that
>> the difference at the 24th bit should be essentially inaudible ... or
> that,
>> if audible, the rounding should sound better than the truncation, but
> the
>> opposite was true.
>
> This is the crux of what I was really asking.  If diddling with the 24th
> bit is audible, then certainly diddling with the 16th bit would also be
> audible (as Steve Pope asserted).  I still find it hard to believe.

I am also a doubting Thomas, but I'm willing to leave some room for 
self-doubt (just not a lot).  I do know that truncation can do funny 
things as the frequencies in the signal beat with the truncation as well 
as each other, producing non-linear distortion.  But at -144 dBFS it is 
hard to imagine it would be in any way audible.   In 16 bits (-96 dBFS) 
I'm willing to acknowledge magic ears can hear it easily (my ears are 
far from magic).

It is always possible that there was some flaw in the original design 
that got fixed when switching to rounding.  I just can't imagine anyone 
can hear the effects of 24 bit arithmetic.

-- 

Rick

Cedron <103185@DSPRelated> wrote:

>This is the crux of what I was really asking.  If diddling with the 24th
>bit is audible, then certainly diddling with the 16th bit would also be
>audible (as Steve Pope asserted).  I still find it hard to believe.

Well suppose you have 16 bits of quantization, and you have a mostly
tone-like signal that is -60 dBc relative to full scale.  This signal only
has 6 bits of precision, so its quantizing noise is only about -36 dB
relative to the signal, and that may not be far enough down for
it to sound the same in the dithered vs. undithered cases.

Note that many acoustic musical instruments have much more than 60 dB
of dynamic range ... try 90 dB or 100 dB or more for a piano (they
don't call it a pianoforte for no reason) or various percussion instruments.
Not to mention combinations of quiet and loud instruments.  If you are
trying to capture these dynamic ranges, and also maintain good quality
for the quietest passages, 16 bits is marginal in the first place,
and even more marginal if it's undithered.

Steve

On 5/6/2015 12:49 AM, Steve Pope wrote:
> Cedron <103185@DSPRelated> wrote:
>
>> This is the crux of what I was really asking.  If diddling with the 24th
>> bit is audible, then certainly diddling with the 16th bit would also be
>> audible (as Steve Pope asserted).  I still find it hard to believe.
>
> Well suppose you have 16 bits of quantization, and you have a mostly
> tone-like signal that is -60 dBc relative to full scale.  This signal only
> has 6 bits of precision, so its quantizing noise is only about -36 dB
> relative to the signal, and that may not be far enough down for
> it to sound the same in the dithered vs. undithered cases.

The issue is not how many bits are used for the signal, but how many are 
used for the noise.  With 16 bits, yeah, you may hear the difference. 
But at 24 I just can't see how you would  ever hear it.  I'd bet that if 
you fed a 1 bit tone into a 24 bit ADC with the volume on the amp at a 
normal listening level you can't hear the tone at all.  If I felt like 
digging my test fixture out and writing some code to test it, I could 
demo it... but it would be with my barely working ears.


> Note that many acoustic musical instruments have much more than 60 dB
> of dynamic range ... try 90 dB or 100 dB or more for a piano (they
> don't call it a pianoforte for no reason) or various percussion instruments.
> Not to mention combinations of quiet and loud instruments.  If you are
> trying to capture these dynamic ranges, and also maintain good quality
> for the quietest passages, 16 bits is marginal in the first place,
> and even more marginal if it's undithered.

Yeah, but what was being discussed was rounding vs. truncation of 24 bit 
values.

-- 

Rick

Cedron <103185@dsprelated> wrote:

(snip)
> This is the crux of what I was really asking.  If diddling with the 24th
> bit is audible, then certainly diddling with the 16th bit would also be
> audible (as Steve Pope asserted).  I still find it hard to believe.

As far as I know, it is very difficult to build amplifiers with
the 140dB S/N that would allow one to hear the 24th bit. Probably
it would make more sense at 20 bits (40 for a stereo sample) but
that doesn't seem to be what is done.

-- glen

rickman  <gnuarm@gmail.com> wrote:

>The issue is not how many bits are used for the signal, but how many are 
>used for the noise.  With 16 bits, yeah, you may hear the difference. 
>But at 24 I just can't see how you would  ever hear it.  I'd bet that if 
>you fed a 1 bit tone into a 24 bit ADC with the volume on the amp at a 
>normal listening level you can't hear the tone at all.  

Well, that isn't the only scenario in which a 24-bit signal might
get used.

The real point is, when you quantize from analog and/or reduce precision,
dithering is wise.  If there is not already enough noise in the 
source signal to auto-dither the thing, then add explicit dithering.
Don't waste brain cycles arguing "it might not matter", just do it,
unless the cost is prohibitive, which it almost never is, especially
in audio.

If you've got a K-band radar signal you are debating whether to 
dither, then that is a plausible debate.  At audio it's a no brainer.


Steve

glen herrmannsfeldt  <gah@ugcs.caltech.edu> wrote:

>As far as I know, it is very difficult to build amplifiers with
>the 140dB S/N that would allow one to hear the 24th bit. Probably
>it would make more sense at 20 bits (40 for a stereo sample) but
>that doesn't seem to be what is done.

We used to build amplifiers that outputted +28 dBv with an
input noise over 20 KHz of -130 dBv.  Professional audio
equipment may not need that range, but can certainly use the
range because it's convenient that you don't have to worry
so much that a given signal in the mix is either overdriving or
underdriving an amplified stage.

To do this, we sorted transitor pairs on a noise station
and similar tedious tasks.  It was not difficult, but it
would not be my first choice of job right now.


Steve

On 5/6/2015 1:44 AM, glen herrmannsfeldt wrote:
> Cedron <103185@dsprelated> wrote:
>
> (snip)
>> This is the crux of what I was really asking.  If diddling with the 24th
>> bit is audible, then certainly diddling with the 16th bit would also be
>> audible (as Steve Pope asserted).  I still find it hard to believe.
>
> As far as I know, it is very difficult to build amplifiers with
> the 140dB S/N that would allow one to hear the 24th bit. Probably
> it would make more sense at 20 bits (40 for a stereo sample) but
> that doesn't seem to be what is done.

Maybe I am misunderstanding what you are saying.   You don't add 
dithering to make anything audible.  You add the dithering so the 
truncation does not inter-modulate with the signal.  Instead of getting 
tones from the quantization or truncation, adding the minimum amount of 
dither (1 lsb max) spreads the noise over the full range of frequency 
making it much lower than the tones you would get otherwise.

-- 

Rick

On Tue, 05 May 2015 17:46:00 +0000, Eric Jacobsen wrote:

> On Tue, 05 May 2015 12:02:41 GMT, N0Spam@daqarta.com (Bob Masta) wrote:
> 
>>On Mon, 04 May 2015 22:43:01 GMT, eric.jacobsen@ieee.org (Eric Jacobsen)
>>wrote:
>>
>><snip>
>>
>>>I haven't seen anybody claim that to be true for even a new Ferrari or
>>>Porsche yet, but I suspect they're getting close.
>>
>>My engineering career started back in the early '70s at GM's Cadillac
>>division.  One epiphany from that was the huge engineering advantage of
>>high production volumes. I was surprised to discover that Roll Royce,
>>Lamborghini, etc bought GM transmissions. But when you are only turning
>>out a handful of cars per year, you can't afford a huge engineering
>>staff for just one part of the car.  Even more important, you can't get
>>decent field data on failure modes so you can improve your product.
> 
> It's interesting that for a lot of the performance technology, including
> things like ABS, stability control, active handling, and
> performance-optimized traction control, the technology often comes from
> ultra-low volume race applications.   Companies that have big race
> efforts as part of their core, like Ferrari, McLaren, Porsche, Honda,
> Audi, etc., etc., and in this case specifically GM with the Corvette
> (and also Cadillac lately), the technology gets developed or really
> optimized as part of the racing effort.


One racing innovation that I found fascinating (and also related to 
filter design, keeping it on-topic) is the "inerter".

Suspension designers use filter synthesis techniques borrowed from 
electronics.  They often use the "Mobility analogy" :

 mass == capacitance to ground
 spring (or tyres) == inductor
 shock absorber == resistor

One can synthesise low pass filters using the usual method(s) for analog 
filter design.  But to get sharper rolloffs, e.g. as in an elliptic 
filter, the designer needs a pair of zeros on or near the jw axis.  In a 
filter, that is done with a series element consisting of an inductor in 
parallel with a capacitor.
Can't be done mechanically as there isn't a mechanical element analogous 
to a "flying" (i.e. ungrounded) capacitor ... that is, until someone 
invented the "inerter".  Amazingly, this didn't happen until early this 
century.


"Flying" capacitor in parallel with inductor giving transmission zeros:
http://en.wikipedia.org/wiki/File:RLC_parallel_band-stop.svg

"Inerter":
http://en.wikipedia.org/wiki/Inerter_%28mechanical_networks%29

Regards,
Allan

On Tue, 5 May 2015 20:52:03 +0000 (UTC),
spope33@speedymail.org (Steve Pope) wrote:

>Cedron <103185@DSPRelated> wrote:
>
>>Is the dither significant soundwise?  In other words, can you hear the
>>difference with or without?  It would seem to me if you were merely
>>shifting a certain number of bits, or dividing my some factor, the lowest
>>order bit wouldn't really matter.
>
>The difference between dithered and undithered quantizing is
>definitely audible on constructed test signals (e.g. tones).
>Undithered quantizing creates correlated noise, which on
>a single tone signal is readily audible, even at 16 bits precision.
>The "noise" becomes tone-like, resembling (a) beat frequency(ies).
>
>Whether it would be audible on a real-world signal, I can't say.
>But if there is no cost or low cost to add the dithering, then just
>dither it since it is one less thing to worry about.

From what I recall, Back In The Day the need for dither was
first noted on long piano decays at the end of a track,
where instead of fading smoothly into the noise floor you'd
hear a buzz  just before fade-out.  As I recall, this became
a problem only when the S/N improved so much that
self-dither wasn't taking place.  (Sony, I think, was first
with this.)  All this was in the 16-bit era.

So yeah, definitely needed on real-world signals.

Best regards,


Bob Masta
 
              DAQARTA  v7.60
   Data AcQuisition And Real-Time Analysis
              www.daqarta.com
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On Tue, 5 May 2015 16:06:27 -0700 (PDT), Greg Berchin
<gjberchin@charter.net> wrote:

<snip>
>
>In an old issue of Stereophile there is an article describing what a certai=
>n high-end manufacturer did to change one of their DAC products from an ave=
>rage-sounding product to a superior sounding product. I don't remember the =
>exact context, but I do remember the change: the switched to rounding at th=
>e 24th bit to truncating at the 24th bit. Conventional wisdom said that the=
> difference at the 24th bit should be essentially inaudible ... or that, if=
> audible, the rounding should sound better than the truncation, but the opp=
>osite was true.

Count me among the skeptics on this.  First, I seriously
doubt that Stereophile magazine would know *everything* that
the manufacturer did in the change, and I'd be more inlined
to think it was something else that turned the tide... I'd
guess even the semi-mythical capacitor replacement would
have a higher audibility.

But the other issue (steps back on soapbox) is whether this
dramatic change was verified by double-blind testing. <g>

Best regards,


Bob Masta
 
              DAQARTA  v7.60
   Data AcQuisition And Real-Time Analysis
              www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
 Frequency Counter, Pitch Track, Pitch-to-MIDI 
   FREE Signal Generator, DaqMusiq generator    
          Science with your sound card!