Xref: utzoo sci.electronics:12961 rec.audio:22955
Path: utzoo!attcan!uunet!island!rich
From: rich@island.uu.net (Rich Fanning)
Newsgroups: sci.electronics,rec.audio
Subject: Re: Digital/Analog converter help needed
Summary: need a multiply for volume.
Message-ID: <1839@island.uu.net>
Date: 18 Jul 90 20:07:41 GMT
References: <3550.26a1d2d7@ccvax.ucd.ie>
Reply-To: rich@island.uu.net (Rich Fanning)
Followup-To: sci.electronics
Lines: 25

In article <3550.26a1d2d7@ccvax.ucd.ie> b_haughey@ccvax.ucd.ie (Brian J Haughey) writes:
>What I am looking for is info on D-A converters that can directly drive
>speakers. My query is : would the scaling factors of such a D-A have
>to change as the volume went from very low to very high ?

I'm not exactly sure what you want here.  You say "D-A converters that
can directly drive speakers".  By this do you mean a "digital amplifier"?

There are at least two ways to do this: convert D/A at a one-volt, high
impedance level, and amplify in analog.  Or amplify the digital signal pulses,
send through a filter to round off all those nasty sharp edges, and out
to the speaker.

Either way, it would probably be desirable to multiply the 16-bit audio
coming in by a scale factor which represents the "volume".
Given fast enough hardware, it would probably be reasonable to do a
"brute force" approach:  represent the volume by a 16-bit value, and multiply
the 16-bit audio signal to get a 32 bit result.  Take the top 16 bits,
and there's your scaled digital signal.

No doubt, there are more efficient ways to do it.  And a simple multiply
does not take care of rounding problems.  How do professional digital mixers
do it?
-- 
	 Rich Fanning         {sun,ucbcad,uunet}island!rich