audio playback with variable tempo

Gary Aitken ah at
Thu Dec 13 23:56:59 UTC 2012

On 12/12/12 23:51, Polytropon wrote:
> On Wed, 12 Dec 2012 16:27:16 -0700, Gary Aitken wrote:
>> Can anyone suggest an audio playback application that allows you to vary the
>> tempo?  I've used audacity on win systems, but I don't see that in ports.
> Except that audacity actually _is_ in ports, if you just
> require "adjustable" speed (without editing / saving the
> original file), you could use "mplayer -speed <n> <file>",
> or use "mplayer <file>" and use the [ ] and { } keys to
> adjust the speed (if you have OSD on, key 'o') you can
> see the speed (if the file contains video; if not, the
> output will be text only for information purposes).

Speed is not what I want to adjust, as it changes the pitch.
The playback timing needs to be adjusted so everything has the same pitch,
but just comes out faster or slower.

Found audacity and got it installed and working great.

However, I'm a little confused on what all the devices are related to audio.

For the default device, which I've set to unit 3 (for pcm3), 
I see the following in /dev:  dsp3.0 mixer3
What are each of these associated with?
The mixer itself shows the following devices:
  vol, pcm, mix, rec, igain, ogain, monitor
Can someone point me to documentation on what these are and how they interact?  
It's not obvious to me what the difference between vol and ogain,
or rec and igain, are, for example.  What is mix mixing, and what does 
monitor do?  A schematic would be helpful...

For device /dev/dsp4, there is a dsp4.0 and dsp4.1, 
which I thought would be the separate left and right channels;
but I only see a dsp3.0, not a dsp3.1, and there is definitely stereo sound.
pcm3 is an analog device, and pcm4 is digital; 
does that have anything to do with it?

Thanks for any enlightenment


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