Re: Stereo > Mono Downmixing on iOS
Re: Stereo > Mono Downmixing on iOS
- Subject: Re: Stereo > Mono Downmixing on iOS
- From: Paul Davis <email@hidden>
- Date: Thu, 31 Mar 2011 19:25:46 -0400
On Thu, Mar 31, 2011 at 7:16 PM, Roman Thilenius <email@hidden> wrote:
> when i was suggesting to use 1 overflow bit per channel that was
> more like a philosophical answer to the thread starter, paul is
> right that you will normally just use float to sum 2 channels,
> even ikf the source was int24.
>
> either the material you sum is already float, or it is not, and if
> it is not, of course a 25th bit will definetly be enough to sum
> them - yet an engineer still dont do that in practice, because it
> is hilarious to convert your 24 bit vectors into 25 bit vectors only
> to make sure that you do not clip 3 samples per piece of music -
> and that in a personal computer OS or phone OS enviroment. ^^
i don't consider any environment that doesn't use float as its
standard format for handling samples as suitable for 3rd party audio
software development. nobody would dream of converting from 24 bit to
float *just* for summing. if you're not already using float, then you
need to solve how to *add* the samples without overflow in whatever
format you're using. if you are already using float, there is no
problem with the *addition* that needs solving.
bob is right of course that at some point the summed value will go
back through a converter that expects only N bits, and if the summed
value overflows that bitwidth, you still have to solve that problem.
but this is true no matter what format you are using.
it is a little hard for me to believe that in 2011, anyone is having
this discussion on a mailing list, let alone this one. as brian
pointed out, there is no single approach to summing samples that is
right for all cases, but this is audio programming at its most basic,
and this is a problem that has been mapped out and clearly understood
for at le
> but about float ... well, there IS a difference. using float32 to sum
> up 2 float 32 channels which do not exceed 1.0 literally gives you
> _many "overflow bits" - and not just the _one per channel which i
> suggested as theoretically required.
>
> when you think about summing in a DAW, the chaos theorem will
> explain why float 64 should normally be enough to mix rock music,
> even if the user really runs 400 tracks.
> only in theory you need one overflow bit (as in "bits of precision")
> per channel, but not in real life.
>
> even if the threadstarter wants to sum 2 channels of int 24, doing the
> math in int 24 with no headroom at all should be just fine in practice.
>
>
> -110
>
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