Better Programming!

As promised in Chapter 2 of SOUND EFFECTS, I will talk about the Noise channels for this month.

The Noise Channels are opened by using the register 7. You substract to 63, 8 for Channel A, 16 for Channel B and 32 for Channel C. A new register is now used, register 6. This register is somewhat the frequency of the noise, the higher the value, the lower the frequency.

The noise channels are mainly used to create the sound of rockets, explosions, everything that make noise instead of music!

You may enable all 3 Music channels and all 3 Noise channels at the same time by giving the value 0 to the register 7. If you only want the 3 Noise channels, put the value 7.

Usually, when using the Noise channels, you enable the Envelope generator to create the effect desired. The Envelope generator works the same way for the Noise channels as it does for the Music channels. To enable the Envelope generator for Noise channel A, you would put the value 16 to the register 8 and for channel B, you would put 16 to the register 9, etc…The only inconvenience with this is when using Music channel A and Noise channel A at the same time, if you enable the Envelope generator for one the other will be affected as well!

To avoid this, especially if you are only using 1 or 2 Music channels, you put the Noise effect on the third channel. But don’t get me wrong, you cannot create two envelopes (see last issue) at the same. If you do need two envelopes you will have to either wait until the first effect is over and start the second after or if you play music while, say…, a rocket flies through the screen, just put the envelope to the music and none for the rocket or the other way around, if you wish (usually the music doesn’t need any envelope).

Don’t forget…

Music channel A you add 1 to your total
Music channel B, add 2
Music channel C, add 4
Noise channel A, add 8
Noise channel B, add 16
Noise channel C, add 32

Then you put the value 63-total to the register 7…

You cannot use 2 different envelopes at the same time!

Use the value 16 to enable the Envelope generator…

8,16 for channel A
9,16 for channel B
10,16 for channel C

…Use register 11, 12 and 13…

Register 13 is the envelope shape.

Register 11 and 12 are the FINE and COARSE tune envelope periods.

…Use register 6 for Noise frequency…

Higher value = lower frequency.

Well, that’s it for this month! Next time I will show you how to make an echo when playing music.

So join me next month for Chapter 4 of the SOUND EFFECTS!