Mixing it together

In the analog drums project, altogether 10 sound generators have now been breadboarded and tested. I think now it is time to stop collecting various nice sounding generators and start to figure out how these will be used together.

After some thinking and wondering, I came up with the overall structure of the drum machine like this. Here I’m assuming that all 10 sound generators are in use:

 

 

 Basic principles:

  • Noise generator is common to all sound generators needing noise.
  • Sequencer has as many trigger channels as there are sound generators + 1 for accent.
  • Each sound generator has two outputs: one for normal sound and one for accent.
  • Each sound main output goes to main mixer through channel’s own level control.
  • Each generator’s accent output goes to accent mixer.
  • The mixed accent signal goes to accenter circuit and from there to main mixer through the accent level control.
  • Main output level control is after the main mixer.

The accent output in the sound generators is often the same signal as the main output, meaning that the accent simply rises channels volume for a short time in the start of the accented beat. In some generators, especially hi-hats, there is a simple high-pass filter before the accent output, so that higher frequencies get accented more than lower. I stole this idea from Boss, hard to say how much it will have effect on what is actually heard.

The accent functionality is very basic: because all accent outputs are mixed together and there is only one accent channel, accenting happens to all sounds which are triggered simultaneously with the accent channel. Again, this principle is taken from Boss and I think it is widely used, because channel-specific accents would make things much more complicated.

I’m not sure whether the accent functionality is worth all the hassle, because big part of the complexity seems to come from it. But I’m not giving up yet, let’s see where it leads.

At least one thing needs still consideration: although I have not yet decided anything about the sequencer part, it seems quite clear that the sequencer cannot not have 11 channels, it will be too complicated. Either some of the sounds have to be dropped or there must be channels with selectable sounds. But I don't like the idea of dropping those nice sounds I have found an tested.

If we think about selectable sounds, it would be quite obvious to make the two bass drums, two snares and two hi-hats each selectable on their own channels. You very seldom need two of the same sounds at the same time. Also rimshot and claves would be kind of sounds that might be possible to combine to one channel. After that there would be 7 sequencer channels: 6 sound channels + accent channel. The amount of channels starts to sound reasonable.

This reduction does not change the picture above much, only the “10”s change to “6” and selection switches will appear to some of the generator trigger and output signals. Now this is beginning to look like a structure that could be implemented.

 

In the next post I'll take this all to more concrete level by designing and building some printed circuit boards.


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