On Fri, 2011-03-11 at 10:52 +0000, Richard Lewis wrote:
At Thu, 10 Mar 2011 18:26:38 +0000, Adam Bower wrote:
On Thu, Mar 10, 2011 at 05:49:22PM -0000, Ted Harding wrote:
The nub of my query: is there a program which will play an audio CD, with an option which allows the pitch to be shifted?
Rip the audio and then adjust pitch in software and play back without the CD?
I would definitely agree that processing audio once it's been copied from the CD will be much easier.
Recent versions of Audacity http://audacity.sourceforge.net/ include a plugin for pitch shitfting.
Also, the rubberband library http://breakfastquay.com/rubberband/ has quite a good reputation amongst my colleagues. It includes a command line utility http://breakfastquay.com/rubberband/usage.txt
There is more than way to shift the pitch depending on whether or not you want to keep the speed the same.
My understanding is that in a standard CD player a reference clock is available at the sampling frequency, 44.1Khz or a multiple therefore and the speed of the motor is continuously adjusted to get samples to come off the disk at that rate and go though the D/A converter at that same rate. If the reference clock was adjusted the CD would naturally play the disk a different rate and also change the pitch just like changing the speed of a vinyl record.
The same trick can be done if the signal has been digitally extracted though now this involves resampling. You can do this on the command line by taking a wav file, converting to raw with 'sox' and then converting back to WAV and resampling at the same time and lying to SOX about the sample rate of the RAW file. The result is both a pitch shift and a speed change.
To change the pitch and keep the speed constant involves heavier DSP and with more risk of artifacts. This is what rubberband does. Rubberband is used in ardour, an open source digital audio workstation for Linix and MacOS (http://www.ardour.org/).
On the hardware front CD players designed to play CD-G disks for Karaoke usually have the option of changing the key of the backing to suit the singer though on many this is only in semitone steps, not continiously adjustable. These same players will play normal CDs but obviously without any associated graphics.
CD players designed for use by DJs in clubs often enable the playback speed to be adjusted though I don't know whether this usually affects the pitch or not.
Steve.