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From: ncpjmw@brahms.amd.com (Mike Wincn)
Newsgroups: sci.electronics
Subject: Re: Digital/Analog converter help needed
Message-ID: <1990Jul24.215643.22718@amd.com>
Date: 24 Jul 90 21:56:43 GMT
References: <3550.26a1d2d7@ccvax.ucd.ie> <1839@island.uu.net>
Sender: usenet@amd.com (NNTP Posting)
Organization: Advanced Micro Devices; Sunnyvale, CA
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In article <1839@island.uu.net> rich@island.uu.net (Rich Fanning) writes:
>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
[...]
>There are at least two ways to do this: convert D/A at a one-volt, high
>impedance level, and amplify in analog. 

Well, yeah, maybe... though I haven't heard of any 100w DACs anywhere yet.

>Or amplify the digital signal pulses,
>send through a filter to round off all those nasty sharp edges, and out
>to the speaker.

THIS idea hasn't a snow-balls chance in hell of working!  Think! ...how in
hell do propose to sum up all those digital pulses to reconstruct the 
analog program material before sending it to the load?

>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.

Indeed, though one might have an easier time of it if one started with the
16 bits as the full range of a DAC (max output), and shifted towards the LSB 
end for attenuation, though that will only give you a factor of 2 control.  For
more precise control, amplitude interpolation will be necessary.

Mike Wincn
(408) 749-3156
ncpjmw@brahms.AMD.COM