Subject: From: Date:

Re: [ECS] Low modem Record level Dario Greggio Sun, 04 Jun 2000 11:25:29 +0200

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Mark Gilmore wrote:
> 
> A while back, I spent a lot of time searching for
> a utility pgm that would add gain to an existing
> .WAV, but I could never find one that did NOT
> require some user-interaction.
> Perhaps one of you could give it a try.
> If we can find one, I can have ECS execute
> automatically after recording phone messages.

Hi Mark, I know you don't like such things written in C, but I'm sending
it anyway... :-))

This function takes a bunch of samples (8 bit, mono) "s", whose length
is "l", and gives you back in a buffer called "d" the samples amplified
or reduced by "level" (percentage). In fact, level=100 does nothing.

If you need to start from a WAV file rather than the raw samples, you
should open the file, move to position following "data" plus 4 bytes
(I'm attaching a hex dump of a WAV file from my telephone system) and
from there to EOF execute my function or equivalent.

BYTE *volWaves(BYTE *s,BYTE *d,DWORD l,int level) {
	register int ch;

	if(level==100)
		return d;
	if(!d)
		d=s;
	while(l--) {
		ch=*s;
		if(ch>=0x80)
			ch=(((ch-0x80)*level)/100)+0x80;
		else
			ch=0x80-(((0x80-ch)*level)/100);
		*d=ch;
		s++;
		d++;
		}

	return d;
  }


Hope it helps!

-- 
Ciao,
Dario
--
ADPM Synthesis sas - Torino
--
http://www.geocities.com/adpm99

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