playing u-Law 11kHz files on D/4PCI -voice quality

From: "Martin Steer" <info@eurovoice.co.uk>

Stefan,

Wav or Vox itself won't make any difference in the quality - that just defines the file format / header info on disc.

What will make a difference is to use u-law or A-law companding ... In simple terms this allocates a non-linear mapping of bits to amplitudes so that there are more bits to represent low signal amplitudes, thus reducing the signal to noise ratio caused by quantisation of the analogue signal. It will give a perceived quality equivalent to about a 12-bit linear signal. And this is the standard used by telco's with an 8KHz sampling rate throughout the phone network.

So, assuming your speech is going out over the telephone network, you will get the best quality using u or A-law encoding sampled at 8KHz. This will be better than linear at 8KHz.

As for 11KHz - this will sound better over a soundfile as you will hear frequencies greater than the 3.4KHz upper limit of the telephone network (which is determined by the default 8KHz sampling rate of the network itself) - but when heard over a phone network you should not notice any perceivable difference between 8 and 11KHz sampling.

Just one point worth mentioning though ... 8KHz u-law or A-law wav files are not 'standard' PC wav file formats, so you are unlikely to be able to play them via an ordinary PC without special software or audio codecs added.

Hope that helps!
Martin Steer,
eurovoice limited
http://www.eurovoiceobjects.com

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Received on Wed Oct 29 18:25:05 2003