info-mac@utcsrgv.UUCP (info-mac) (04/26/84)
Date: Monday 23 April 1984 12:02:53 EDT From: Leo Hourvitz <uw-beaver!leo@mit-pamela> Subject: Macintosh Sound Barrier Expounded To: <info-mac@mit-pamela> Finally got my copy of Inside Mac. Here's a summary of what it says about sound. Sorry if it duplicates something you already got. The recommended way to access sound is through the sound driver, part of the installed operating system (i.e., in the ROM). You make Write and Control calls on it, just like all those OSs we know and love. The Write call gives a pointer to a sound record, the first longword of which determines which of the three types of sound generation should be used. If that first integer is negative, the Mac generates square waves (not very interesting). The sound record in this case contains a zero-terminated list of frequency, amplitude, duration integers, which are played in order. If that first integer in the sound record is zero, the Mac begins freeform sound wave generation. You give a waveform table of up to 256 bytes, and a fixed-point duration of each sample in the waveform table, in 44usec units. The Mac plays each of the entries in the waveform table for the specified number of 44usec units, then stops. To generate continuous sound, you perform a write of this type continually. If that first integer in the sound record is positive, you do the interesting sound synthesis, the four-voice engine. This record has, first, the duration (in 16msec units -- I dunno where that comes from) of the sound described by this record. Then, for each of four waveforms, it has the phase and rate (-> frequency) fixed-point integers, and the 256-byte waveform description table. This mode is definitely the most powerful, letting you play and synthesized waveform repeatedley at a selected rate. It is not stated how it combines the four waveforms, though I suspect it adds and clips (I have problems believing it can do any sort of multiplicative combination at that rate). The four-voice engine is the basis of the Mac speech heard at various places. There are three Control calls. One of them sets the amplitude of the square wave generator. Whooppee. Another is KillIO (does the obvious). The third controls the 'three volume bits' on the VIA. I quoth the manual: "Applications shouldn't change the speaker volume, as it's really up to the user to choose the normal sound level via the Control Panel desk accesory." I think that for a hot-dog music program, one would probably ignore the above warning. So, it looks like, just as with the User Interface, one thinks of the sound capabilities in terms of the hardware capabilities + the provided software tools. I suspect that the functions provided by the sound driver are simply to useful, and the ROM/RAM performance differential too high, too allow bypassing the sound driver (not that I'd want to). The sound looks like a source of great fun and kludgery! Let's go. Leo Leo Hourvitz Architecture Machine Group, MIT leo%pamela@mit-mc (Arpanet)
info-mac@utcsrgv.UUCP (info-mac) (04/27/84)
Date: Thu, 26 Apr 84 10:02:22 EST
From: uw-beaver!"Jack Juni"@UMich-MTS.Mailnet
To: PATTERMANN@SUMEX-AIM.ARPA
Subject: Macintosh Sound Barrier Expounded
What's really needed for us SEMI-sophisticated (if that) hackers would be a
short public domain driver rourine(s) accessable from the Mac as it stands
now. Unfortunately, I haven't yet been able to spring for Inside Mac and
I don't have a 68000 assembler. Anyone have any ideas?
Jack Juni (Univ of MIchigan)