ewhac@well.UUCP (Leo L. Schwab) (03/14/86)
[ Replace this line with your line noise ] This may be on the wrong newsgroup, but since I want to do this with the Amiga, it *seems* appropriate. Since the Amiga uses bitmapped waveforms to make sound, how do I create {white,pink} noise? I have a random number generator, but I suspect there's more to it than random numbers. You probably have to get the distribution just right or it won't sound good (I'm guessing). While I'm at it, could someone point me at a good book that will help me not to ask such questions again? Something that will give a guy that knows nothing about sound generation an idea of how to make the noises he wants. Thanks in advance, Leo L. Schwab dual!unicom!schwab well!ewhac "Hello. You've reached my new cellular phone. But I'm not in my car right now, so please leave your name and number after the beep....."
sam@amiga.UUCP (Samuel C. Dicker) (03/15/86)
In article <768@well.UUCP> ewhac@well.UUCP (Leo L. Schwab) writes: > Since the Amiga uses bitmapped waveforms to make sound, how do I >create {white,pink} noise? I have a random number generator, but I suspect >there's more to it than random numbers. Random number generators produce a sound similar to white noise which contains equal energy at all frequencies. This makes a hiss-like sound. Integrating the random number sequence, filters it with a 6db/octave slope (watch out for overflow). This makes a rumbling sound. Pink noise contains equal energy per octave and is the most pleasant noise sound. To produce it, you need to filter white noise with a 3db/octave slope. This is very difficult. I have produced narrow-bandwidth filtered noise sounds on the Amiga by playing a sine wave in one audio channel and modulating the period with another audio channel. The Audio Hardware chapter of the Amiga Hardware Manual explains how to attach audio channels. If the period table is generated by a random number generator and the periods are in a good range (between 124 and about 400) you can produce good quality filtered noise. The center frequency and bandwidth can be controlled by the range of the random period table. You can also modulate other waveforms besides sine waves. Try modulating a waveform which is the sum a sine waves one octave apart ( sine(t) + sine(2t) + sine(4t) + ...) over a one octave period range (like 125 to 250). It might make pink noise. I haven't tried it. > While I'm at it, could someone point me at a good book that will >help me not to ask such questions again? Please ask questions! I haven't had time to write a sound tutorial, but at least I can answer questions. There are many good books on the subject. These are my three favorites that cover most of the subject: Musical Applications of Microprocessors by Hal Chamberlain (Hayden, 1980) Foundations of Computer Music by Curtis Roads and John Strawn (Cambridge: MIT Press, 1985) Digital Audio Signal Processing by John Strawn (Los Altos, California: William Kaufmann, Inc., 1985) J. A. Moorer's article on signal processing in Digital Audio Signal Processing is a good place to start. Sam Dicker {hplabs,decwrl}!pyramid!amiga!sam