Envelope-to: dave@picks.force9.co.uk
Delivery-date: Mon, 17 Oct 2005 15:55:49 +0100
Message-Id: <6.2.5.6.1.20051017101319.01c38e28@magma.ca>
Date: Mon, 17 Oct 2005 10:54:49 -0400
To: lowfer@lwca.org,  rsgb_lf_group@blacksheep.org
From: Bill de Carle <ve2iq@magma.ca>
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References: <004801c5d038$c38c3960$8d01a8c0@JKA>
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Subject: LF: AFRICAM Ver 5.1
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Having noticed AFRICAM is vulnerable to sound card sampling rate 
errors, I added the
ability to specify the exact (nearest integer) sampling 
rate.   AFRICAM defines its bit
times by counting samples, so if the actual rate was too far off 
nominal the program could
not sync or hold sync. I am always amazed by how far off the actual 
sampling rate is for
some (most?) sound cards.  For example, I just recorded an audio file 
under Windows XP
using Cool Edit, asking for 8000 samples per second.  I input an 
800.0 Hz sinewave
synthesized from a crystal source, then measured the frequency of the 
800-Hz tone in
the recording.  The actual sampling rate turned out to be 8100 
s/s!  AFRICAM defaults
to the following nominal rates:

SB16 or compatible  : 8000 s/s
ESS688 chip based  : 8200 s/s
Sigma-Delta board    : 7200 s/s

If you can measure the *true* sampling rate of your sound source and 
type it in, it will
help considerably in establishing and maintaining proper sync.

One way to get AFRICAM to run under Win-XP is to record an audio file 
off the air, like
the original WOLF.  The desired format is 8 bit unsigned (single 
precision) or 16-bit signed
(double precision) MONO values of raw data sampled at say 8000 
s/s.  Cool edit can do
this: select the raw data (.pcm) mode, and be sure the saved file 
name has an extension
of .AUD.  Then when you invoke AFRICAM, use the "DISK" command line 
parameter -
which tells AFRICAM to take its audio from disk instead of trying to 
talk directly to a sound
card or sigma-delta board connected to a serial port.  That makes Win 
XP happy.  You still
get to type in the exact sampling rate at which the audio was 
recorded (it won't be 8000
unless you get real lucky).  In a pinch, you can record a 16-bit MONO 
.WAV file at 8000 s/s
and just change the file extension from .WAV to .AUD before passing 
it to AFRICAM.  That
way the first 40 or so words of the file (.WAV header) will be 
treated as audio samples when
they are not, but it doesn't matter too much.

Version 5.1 of AFRICAM is available from my web site:

http://www.magma.ca/~ve2iq

Good luck!
Bill VE2IQ