[Pdmtl] [PD] 24 bit causing distortion

Mathieu Bouchard matju at artengine.ca
Fri Aug 12 06:28:41 CEST 2005

On Thu, 11 Aug 2005, Robin Millette wrote:

> > but as i've said before, my ears are only 16bit anyway...so it's not
> > big deal for me.
> You should care about that extra byte if you're mixing a lot of tracks 
> and need more headroom.

In PureData, all mixing is done using 32-bit floats, which are like 
24-bit integers, plus adaptive resolution, so that the effective number 
of bits stays 24 no matter what's the dB. So that's a lot more headroom 
than anything you can get with 24-bit integers. That kind of resolution is 
mostly only useful during processing.

The 24-bit integers would only be for recording to .wav.

Honestly I don't really know what's the fuss about 24-bit recordings.  
Maybe because some company got pushed into higher-end equipment than what
was ever desired, so they created the desire and thus the market. Each bit
of resolution requires 6 more dB of S/N ratio in order to not get masked
by the hiss. Multiply that by just 16 and try to find me a soundcard with
a S/N ratio of 2^16 = 65536 = 96.3 dB (!!!).

And then fetch me an ear with 96.3 dB of S/N.

BTW, one can cheat by recording at a very, very quiet level, and then
playing that real loud. This allows your salesman and/or brother-in-law to
effectively disable the top bits of your 16-bit range, making the 24-bit
recording of the same thing sound so much better.

I must add that if you mix a lot of tracks together then the result still
has to go through the same file, soundcard, loudspeakers, room and ears
than before, and if there are 8 simultaneous sounds playing in the same
frequency band with equal loudness then they compete for the available
amplitude range in a way that each of them needs 3 _less_ bits in their
pre-mixing recordings.

The float stuff of Pd is more useful than that because Pd's DSP is used
for more than just sound: e.g. it is also used for indexing into recorded
sounds, and that needs a lot more resolution (and, in fact, many would say
float32 is not enough for that purpose).

(did i write anything inaccurate here?)

Mathieu Bouchard - tél:+1.514.383.3801 - http://artengine.ca/matju
Freelance Digital Arts Engineer, Montréal QC Canada

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