Re: Stereo > Mono Downmixing on iOS
Re: Stereo > Mono Downmixing on iOS
- Subject: Re: Stereo > Mono Downmixing on iOS
- From: Brian Willoughby <email@hidden>
- Date: Mon, 04 Apr 2011 02:48:39 -0700
On Apr 4, 2011, at 02:24, Richard Dobson wrote:
I would finally note that fixed point or integer processing offers
some widely reported advantages over floating-point, in that such
things as comparisons are exact - no messing about with epsilon
differences, etc. Truncation noise n'stuff can be exactly cancelled
out. So an oscillator iteration function (or filter for that
matter) can sit exactly on the unit circle, never migrating outside
it into overflow. So there is a sense in which integer processing
(when skilfully programmed - not something I know how to do!) can
get more performance out of a smaller word size than the computer
based floating point solution can manage. 64bit words may be
overkill, but the top dsp devices do support accumulators of at
least 48bits, so you can do a full 24*24 multiply. The SHARC (as
used in the Creamware cards) is nominally 32bit but has 40bit
registers, IIRC, and can flip between integer, fixed and float with
a single machine instruction.
I hope that we aren't getting off-topic here, but some SHARC
implementations do indeed have 40-bit floating-point performance with
80-bit fixed-point accumulators.
One prominent Mac-only, CoreAudio-compatible audio device makes a
point of their 80-bit summing.
Brian Willoughby
Sound Consulting
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