🚀 go-pugleaf

In article <367@rufus.UUCP>, drake@drake.almaden.ibm.com writes:
> In article <9508@pitt.UUCP> dcollins@pittslug.sug.org.UUCP (Daniel Collins) writes:
> >I am working on a project where I have to compress a speech signal  
> >by 20-to-1 ratio in real-time.  If 20-to-1 not practical, what are 
> >limiting factors, and what is achievable I will be using an 8 bit ADC 
> >with a 8KHz conversion rate.  

> So from 64 Kbits/second you want to do 20:1 compression, down to 3200 bits
> per second?  Pretty aggressive.

Pretty standard, actually, if you go a bit further to 2400 bps.  You can
get a 2400/4800 bps speech vocoder from a number of places (my former
company, Entropic Speech, Inc, sells one); if you're interested in algorithms,
you can get the government standard LPC-10e algorithm (sorry, I don't
know contacts for this; check out back issues of Speech Technology
magazine).

Speech quality is artificial but usable in many applications.  There's been
great progress recently in "medium-range" (4800 to 12K bps) speech compression;
algorithms in this range, while computationally expensive, now have very
low distortion.  The upper end of this range may soon be used in digital
cellular phones.

It's possible to compress speech to much lower rates, but I haven't heard
anything below 2400 bps that I consider generally usable (though you can
make nice sounding tapes in a lab of 1200 bps systems, they tend to be
very speaker-dependent and lack robustness).

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck