1-Bit Wave File?

[Guest]

Archived from groups: rec.audio.tech,comp.dsp (More info?)

Tachyon <shifty@sidehack.sat.gweep.net> writes:

> On 2004-05-21, Jon Harris <goldentully@hotmail.com> wrote:
>> "jim" <"N0sp"@m.sjedging@mwt.net> wrote in message
>> news:40ae12c8_4@corp.newsgroups.com...
>>>
>>>
>>> Randy Yates wrote:
>>>
>>> > The noise will be high, but my intuition tells me you will be able to hear
>>> > the signal (at least one that is at a high level) in the noise. Almost
>>> > certainly one would be able to hear a full-scale sinewave in such noise.
>>>
>>> Why would the scale of the sine wave make any difference or maybe I
>>> misunderstand what you're saying.
>>
>> It is simply a signal-to-noise ratio issue. Much noise is added by the
>> dithering/quantizing process. If the original signal is quite loud, it will
>> still be recognizable above the noise floor. If it is very low level, it will
>> be further buried by the noise. I did a quick experiment, and a full scale
>> sinewave quanitzed with dither was easily heard. I decreased the level and
>> somewhere around 20-30dB down, you really start to lose it. I was actually
>> suprised by how low you could go and still make out the tone in the noise.
>
> Here is an experiment I did.
>
> There are 16 repetitions of the well-known 909 kick drum, mixing triangular noise
> in varying amounts and quantizing to 1 bit. Each hit of the drum doubles the
> noise. It's really interesting to look at with a wave editor, as well as to
> listen. At the low-noise version, you hear a "mean" kick sound. At the noisy end,
> you hear more dynamic range and more noise. I personally like it best with
> about 3/4 of an LSB added. BTW, the subjective volume seems quieter when
> more noise is added:
>
> http://www.gweep.net/~shifty/audio/1bit/reduction/re02.wav
>
> best listened to in loop mode!!

Cool! But... You made the dang thing so short! I mean, bszzzt and it's done!
--
% Randy Yates % "Rollin' and riding and slippin' and
%% Fuquay-Varina, NC % sliding, it's magic."
%%% 919-577-9882 %
%%%% <yates@ieee.org> % 'Living' Thing', *A New World Record*, ELO
http://home.earthlink.net/~yatescr

 

[Guest]

Archived from groups: rec.audio.tech,comp.dsp (More info?)

Randy Yates wrote:
> "Geoff Wood" <geoff@paf.co.nz-nospam> writes:
>>
>> I was alluding to the resultant signal being an asymetrical
>> bitstream, like a PWM signal.
>
> I have no idea what you mean.
>

That's for sure. It was a jest. You may end up with something like:

001001000000110111111100011111111110000

.....which looks to me like a PWM signal, that clearly has no relationship
whatsoever to the original signal.

Yes I know that a serial bitstrem is not what goes into a DA or out of a PCM
word . It was a jest, but equally validly pointing out the silliness of the
"1-bit' sound quality suggestion.

geoff



>> Though I did qualify that it bears no relationship to any
>> encoded signal.
>
> What is "it"?
>
>> One "1", followed by one "0", then two "1"s followed by a "0" looks
>> PWM to me.
>
> How so? It doesn't match any definition of PWM that I know of. When I
> talk about PWM, I mean, e.g., the type of signal shown in figure one
> of
>
> http://www.embedded.com/story/OEG20010821S0096

 

[Guest]

Archived from groups: rec.audio.tech,comp.dsp (More info?)

Jon Harris wrote:

> "jim" <"N0sp"@m.sjedging@mwt.net> wrote in message
> news:40ae9845_6@corp.newsgroups.com...
>
>>
>>Jon Harris wrote:
>>
>>
>>>>They *WON'T* have the same SNR. THAT'S THE POINT!
>>>
>>>Right! Halfscale with have 6dB less SNR than full-scale.
>>
>>Not necessarily. Its perfectly possible that the same bit pattern will result
>>from both input sequences or an even cleaner one from the half scale if the
>>full scale contains more noise.
>
>
> I thought we were talking about the difference between full-scale and half-scale
> sine waves?
>
>
>>I guess your assuming that quantization error
>>is the only source of noise in the original signal. Even if that were true the
>>difference in error from half-scale to full scale is insignificant compared to
>>the amount of error added when going down to one bit - so few bits will end up
>>different that you won't be able to hear the difference. If I understand
>>Randy's dither algo the amount of dither added decreases proportional to the
>>final bit depth.
>
>
> I think you have that backwards. The fewer bits, the more dither you need, so
> dither is inversely proportional to final bit depth.
>
>
>>Again that means when you get down to one bit so few bits
>>will be changed you won't be able to hear the difference.
>
>
> I think you are a bit confused about the way dithered quantization works. Given
> a clean input signal, properly dithered quantization to N bits adds noise based
> on N alone--it is NOT depended on the signal. Now if you quantize a signal
> identical to the first one in every way except 6dB quieter again to N bits
> (assuming the original signal has >> bits than N) you will have the same amount
> of quantization noise, but since the original signal was 6dB softer, you have
> 6dB worse SNR. It really works, I've tried it!
>
> I'll use my analog cassette tape analogy one more time. Imagine recording a
> very low level signal to a cassette tape. Then boost the gain on playback, say
> 60dB. You can still hear the recorded signal, but there is plenty of tape hiss.
> Now imagine doing the same thing again, except with the original signal 6dB
> softer. Boost by the same 60dB and the tape hiss is still at the same level,
> but the original signal is 6dB softer, hence 6dB worse SNR. Dithered
> quantization works THE SAME WAY! The dither (noise) creates a noise floor just
> like tape hiss. (The only difference is that the frequency response of the tape
> noise may be different than the dither noise. In fact, the digital designer can
> choose the sound of the noise floor using noise shaping.)
>
> BTW, that's one of the big breakthroughs about dither--it makes digital sound
> like analog!

Relative to full scale on 15 bits plus sign, one bit is 90 dB down.
bringing that back to full scale is the equivalent of sign extending
down to all the bits. It needs some mental contortions to decide what to
make of it.

Dither is properly done using an amplitude equal to the least-
significant bit. When only one bit is significant, does that mean adding
100% noise? If not, what?

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

 

[Guest]

Archived from groups: rec.audio.tech,comp.dsp (More info?)

"Jerry Avins" <jya@ieee.org> wrote in message
news:40b151a8$0$3126$61fed72c@news.rcn.com...
> Jon Harris wrote:
>
> > I'll use my analog cassette tape analogy one more time. Imagine recording a
> > very low level signal to a cassette tape. Then boost the gain on playback,
say
> > 60dB. You can still hear the recorded signal, but there is plenty of tape
hiss.
> > Now imagine doing the same thing again, except with the original signal 6dB
> > softer. Boost by the same 60dB and the tape hiss is still at the same
level,
> > but the original signal is 6dB softer, hence 6dB worse SNR. Dithered
> > quantization works THE SAME WAY! The dither (noise) creates a noise floor
just
> > like tape hiss. (The only difference is that the frequency response of the
tape
> > noise may be different than the dither noise. In fact, the digital designer
can
> > choose the sound of the noise floor using noise shaping.)
> >
> > BTW, that's one of the big breakthroughs about dither--it makes digital
sound
> > like analog!
>
> Relative to full scale on 15 bits plus sign, one bit is 90 dB down.
> bringing that back to full scale is the equivalent of sign extending
> down to all the bits. It needs some mental contortions to decide what to
> make of it.
>
> Dither is properly done using an amplitude equal to the least-
> significant bit. When only one bit is significant, does that mean adding
> 100% noise? If not, what?

For audio, ideal dither is noise with a triangular probability distribution with
peak-to-peak magnitude equal to 2 LSB's of the new word size. This means, as
you suspected, that a whole lot of noise is added when quantizing to 1 bit! The
theory has been extensively worked out in various AES journal articles and PhD
thesis such as this one: http://audiolab.uwaterloo.ca/~rob/phd.html

 

[Guest]

Archived from groups: rec.audio.tech,comp.dsp (More info?)

Geoff Wood wrote:

> One "1", followed by one "0", then two "1"s followed by a "0" looks PWM to
> me.

Only in a NRZ system...

-- Rick