Re: panning
Re: panning
- Subject: Re: panning
- From: Doug Wyatt <email@hidden>
- Date: Sun, 5 May 2002 14:42:37 -0700
On Sunday, May 5, 2002, at 08:23 , Arthur Clemens wrote:
Hi
I've come across some examples of CoreAudio code that creates a panning
effect for individual channels by iterating n frames over the source
buffer and multiplying each source frame with the left and right volume
values, something like this:
float f;
for (i=0; i<frameCount; ++i) {
f = *sourceBuffer++;
*outBuffer++ = f * leftVolume;
*outBuffer++ = f * rightVolume;
}
I wonder if this is a preferred method.
That's the correct algorithm ... you might find that the code will run
faster by doing two or more samples per loop iteration in order to give
the compiler more room for optimizing with instruction scheduling.
Wouldn't it be better to create a AUGraph for panning?
The problem is I don't really get the concept of AUGraphs, or when to
use them.
From bottom up, we have several layers of audio API's:
CoreAudio - as close as you can get to talking to the hardware for
audio I/O
AudioToolbox/AudioConverter - useful for sample rate conversion,
channel mapping (when
dealing with multi-channel hardware), and format conversions (PCM only
in 10.1, but if you look at the API you'll see that it could
be extended to support
codecs... (as we'll be discussing at WWDC)
AudioUnits
output units - hide some details of talking to the hardware, allow
you to output to the system (alert) and default output devices
effects etc. - reusable DSP plug-ins, some provided by Apple,
developers
can also publish their own
AUGraph
construct arbtirarily complex chains (graphs) of AudioUnits
- for dedicated purposes if you hardcode the AudioUnits used
- allowing user-selectable effects if you allow the user
to choose how the graph
is constructed
You can benefit from AUGraph if you want to leverage AudioUnits provided
by Apple or others, or package your own DSP code in reusable components.
If you have a more highly specialized application, you might have no
need for AUGraph and AudioUnits -- you might just do all your own DSP
and then talk to the hardware or output AudioUnits.
HTH,
Doug
--
Doug Wyatt
work: email@hidden (CoreAudio)
personal: email@hidden
http://www.sonosphere.com
"Don't negate, create."
-- dsw
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| References: | |
| | >panning (From: Arthur Clemens <email@hidden>) |