[LAU] About Algorithms

David Adler david.jo.adler at gmail.com
Mon Jul 18 12:01:35 UTC 2011


On Mon, Jul 18, 2011 at 12:56 PM, Erik de Castro Lopo wrote:
> David Adler wrote:
>
>> On Mon, Jul 18, 2011 at 12:13 PM, Renato wrote:
>> > On Mon, 18 Jul 2011 11:53:47 +0200
>> ...
>> > isn't it useless going way above 24 bits, since that's what in the end
>> > the DAC (sound card) will use? as far as I can remember, delta-sigma
>> > DACs don't go over 24 bit, do they?
>> >
>> More than 24 bit for DAC/ADC is useless, going above 24 bit for
>> internal processing is not. The latter ensures that rounding errors
>> that may be introduced by multiple math operations disappear when bit
>> depth is finally reduced again to 24 before entering the DAC.
>
> Do not confuse DAC/ADC bit width with bit widths used during DSP
> calculations. The two are basically orthogonal.

How did I confuse them?

>> The magnitude of rounding errors depends on the type and number of
>> operations done. I don't know the limits, but for what Fons calls
>> "normal audio engineering practise" (see his posting above), 32 bit is
>> enough.
>
> For audio data paths this is true. For the intermediate results
> during complicated calculations (eg filters and reverbs) double
> precision makes things easier and is basically available for free.

Oui, I stand corrected.


best,
d


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