d6maca@dtek.chalmers.se (Martin Carlberg) (07/27/90)
I want to generate sounds consisting of two simultaneous tones of different
frequencies (the sounds generated by a touchtone telephone). Reading Inside
Macintosh about the Sound Manager I find out that I would probably get the
desired effect by using the wave table synthesizer, which can deliver up to
four simultaneous tones. There is a Sound Manager command called freqCmd where
IM says: "If no sound is playing, it causes the synthesizer to begin playing
at the specified frequency for an indefinite duration." and "A frequency value
is sent in the lower three bytes of param2, where the frequency desired is
multiplied by 256."
This is fine for me, I create two channels using the wave table synth, makes a
sine wave table, and send one freqCmd to each channel, and sound doesn't
stream out of my speaker.
It's very quiet (well, there is a fan and a hard disk in my Mac).
This is a piece of Pascal code that does not produce sound:
PROGRAM Frequency;
USES Sound;
VAR channel: SndChannelPtr;
firstCmd, secondCmd: SndCommand;
FUNCTION SineWave: Ptr; EXTERNAL; { Makes nice waves }
PROCEDURE BombOnError (result: OSErr); EXTERNAL; { Tests for error }
BEGIN
channel := NIL;
BombOnError (SndNewChannel (channel, waveTableSynth, 0, NIL));
firstCmd.cmd := waveTableCmd;
firstCmd.param1 := 512;
firstCmd.param2 := LONGINT (SineWave);
BombOnError (SndDoCommand (channel, firstCmd, TRUE));
{ The following should start a continious sound }
secondCmd.cmd := freqCmd;
secondCmd.param1 := 0;
secondCmd.param2 := 440 * 256;
BombOnError (SndDoCommand (channel, secondCmd, TRUE));
WHILE (TRUE) DO; { Sound forever... }
BombOnError (SndDisposeChannel (channel, TRUE));
END.
It could use the old faithful Sound Driver, but I don't like to use something
that has got a replacement.
Anyone has a clue?
Thanks in advance,
- Martin Carlberg (d6maca@dtek.chalmers.se)
- Chalmers University of Technology, Goteborg, Sweden oster@well.sf.ca.us (David Phillip Oster) (07/29/90)
If you read the restrictions and limitations section of the Sound Manager
chapter, you will see that you can't generate two simultaneous tones (or more)
with it on a MacPlus or an SE. It simply doesn't work. Probably the best
thing to do is check the hardware in SysEnvirons, and if it is an original
mac, a Mac XL, a Mac 512k, 512KE, Plus or SE use sound driver, and use
sound manager for everything else. This should protect you from future
machines failing to implement sound driver, but it is a pain. Since you
have to write the sound driver stuff anyway to get it to work on the 6
machine types I've already listed, and since Sound Driver works on
all current macs, there is a strong temptation to just do it in Sound
Driver and be done with it.
I've dissassembled hypercard, looking to see how it does it. It calls
Sound Driver on all machines, for touch tone sounds.
--
-- David Phillip Oster - Note new signature. Old one has gone Bye Bye.
-- oster@well.sf.ca.us = {backbone}!well!oster