Path: utzoo!attcan!uunet!husc6!mailrus!cornell!uw-beaver!teknowledge-vaxc!sri-unix!larson
From: larson@unix.SRI.COM (Alan Larson)
Newsgroups: comp.sys.mac.programmer
Subject: Sound (mostly freeform)
Keywords: buggy, bummer, misfeatured
Message-ID: <23906@sri-unix.SRI.COM>
Date: 4 Nov 88 11:01:37 GMT
Organization: SRI International, Menlo Park, CA
Lines: 43


I have some questions concerning the sound driver and hardware.

When using the Free From synthesizer, I have discovered that
the values in the waveform correspond to voltage at the speaker
terminal as follows:

	value	voltage on center pin of speaker connector
	 255	most positive value
	 128	zero voltage
	   0	most negative value

After a free form waveform is transmitted, the voltage appears to remain
at the last value sent from the waveform.

At the start of a free form waveform, a brief period of 0 is sent (the
most negative voltage).  Unless the previous value was 0, and the
new waveform picks up smoothly from 0, this causes a click in the speaker.

Calling StopSound() will reset the voltage to zero (value 128), perhaps
with some overshoot (I was watching with a voltmeter, not a scope).
If the voltage was at some different value (such as value 0) from the
previous waveform, this causes a click in the speaker.


This was all discovered on a SE.

I tried running with all waveforms starting and ending at value 0 so there
would be no clicks (there were no StopSound calls).  On the SE, this produced
clean sounds.

I tried running this on a Mac II.  There were clicks audible.  Why?


I tried running the program on a Mac +.  I don't recall if there were
clicks audible between my sounds, but after the last sound was finished,
while polling for a keyboard hit, it produced a fairly loud obnoxious
buzzing sound.  The other machines had not done this.


Can anyone shed some light on this?  Please!

	Alan