[plug] Audio Speed Control

[Simon Scott]

	A couple of things

	a) at the samplerate you are talking about, I would triple check
your code to ensure it does what you think its doing. I cant believe it
would sound that bad. I have written similar code on the Commodore 64,
pushing 8Khz, 4 bit samples through the volume register and it sounded
great.... and I was shifting nearly an octave at times.

	b) Obviously you cant shift it too far, or it will sound crap no
matter what you do.

	c) If it is just noise, I have heard it said that if you introduce
random noise into the sample, it can in fact sound better....  dunno if you
wanna go this far though

	Does it sound better/worse if you shift up/down?

	How are you calculating when to double/drop a sample? 


	At the end of the day, this sort of algorithm will only do so much
before you have to look at resampling which, (to my limited knowledge) is
akin to your linear interpolation but is 'non-linear', if you know what I
mean. But even that might sound crap.






	From:	Brad Campbell <brad at seme.com.au> on 24/10/2001 02:35 PM
	Please respond to plug at plug.linux.org.au@SMTP at Exchange
	To:	plug at plug.linux.org.au@SMTP at Exchange
	cc:	 

	Subject:	[plug] Audio Speed Control

	G'day all

	I have implemented real-time pitch shifting in mpg123, but the
algorithm
	being used (I am using an already existing algorithm in the code)
makes
	for a really rough nasty harsh sound. 
	It simply duplicates or drops samples as required.
	I have tried writing some linear interpolation into it to smooth it
out
	a bit, but it really does not help much.

	Has anyone done any work in this area? Or can you recommend an
existing 
	OSS project that you use, that has a reasonable pitch shift built in
that
	sounds Ok..

	I have tried a couple of xmms plugins, but one sounds rough and the
other
	is not reliable enough to give me a decent listening test.

	The pitch shift in alsa player was not much good last I tried it
either.

	-- 
	Brad....
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