Re: [ecasound] W64 format conversion correctness

Thank you for your response, Kai.

On 5/29/05, Kai Vehmanen <kvehmanen@email-addr-hidden> wrote:
> On Fri, 20 May 2005, Free Lunch wrote:
>
> Before processing, ecasound converts all input data to its internal format
> which is 32bit float atm.

Just to clarify, is that true for cases when recording from alsa with
ecasound? Does data coming in at 24 bits get converted to 32b and
back to 24b before being written to disk?

> Neither ecasound or libsndfile supports dithering (although it is on
> libsndfile's todo-file and will be utilized by ecasound also when ready),
> so there can be some artifacts from the float->fixed down-conversion.

While dithering would be an improvement, it is a complicated subject
and there are so Many ways to do dithering..

For my audio recording purposes, any conversion is bad. The streams
must be bit-accurate so that the integrity of the audio chain can be
verified.

> Now, but, but... if you don't perform any processing, just plain copy,
> there shouldn't be any artifacts as the result should be
> fixed(A)->float(B)->fixed(A). It's possible that some rounding/truncation
> errors are created by differences in doing the fixed<->float conversion
> between ecasound and libsndfile. You can work around this by using
> libsndfile for all conversions:
>
> ecasound -i sndfile,foo.wav -o bar.w64

Cool! I am again impressed by the flexibility of ecasound.

My initial tests of this method still seemed to show some minor
differences but I need to evaluate it further.

> PS And of course, using more bits per sample will help -- record
> to 32bit-floats if you are really paranoid. :)

I'm not sure that would help when my A/D is only 24 bits. Certainly,
processing should be done with 32 bit floats but the hope is to not do
any processing.

Thanks again!

  FL

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Received on Thu Jun 2 20:15:09 2005