Ok, so time for another setting you might have seen inside you module that you might not be 100% clear about. Lets look at Reject Time.
Lets imagine you put a trigger on an acoustic drum. And lets say (just for fun) its a big, low tuned 16” tom. Now, lets say that you dont change anything inside the module, and you hit the tom. What happens next? What sound comes out of the module? Well, probably, it will go “BRRRRRRRrrrrrrrrrrrrrrrrooooom...” rather than the nice big “Boom” you were expecting. Why on earth is that happening?
Well, its quite simple. If you recorded the sound of your ringy 16” tom and put the recording on a screen, you'll probably see something like this;
And in that picture you can see the waveform going up and down (about 70 times a second if you can see the time scale at the top of the picture) and gradually dying away.
So, what your module hears when you hit that tom ONCE is you hitting the tom 70 times a second as it sees every time the waveform line goes up as a new trigger. It doesn't know whether you have hit it once or seventy time, it just reacts to what is coming in to the pad input channel. So, we have to help it.
(If you read the last article about Polyphony, you'll also hopefully realise that those 70 notes that the module thinks you have just hit have also just killed your polyphony stone dead – not good)
We know that the threshold removes a lot of problems for us. Simply put, when the trigger signal drops under the threshold level, it is ignored. But when the trigger signal is above it, the module assumes that every waveform rise (where the waveform goes us) is a new trigger signal.
But its not quite that simple. The module will only think a wobbly waveform is a new signal if the rate of rise (ie the angle of the 'up') is steep enough. By the time the signal has died a way a bit, the angle of the ups and downs is quite a bit softer so the module ignores those.
So what do we do? The tom is generating lots of 'hits' which gradually die away, and we dont want those to trigger the sound again as it will be an audio mess.
So we use the Reject Time parameter. Reject Time (or Mask Time as it is also called) turns the input off after it has received a trigger input, to allow for the vibrations to (hopefully) calm down a bit, prevent miss-trigger, and so make the module's job a bit easier.
We measure the Reject/Mask Time in milliseconds (ms) as in the real world, its only the first little bit of the low, wobbly tom sound that is the most confusing for the module. After that, hopefully the waveform has died down enough for the module to ignore the waveform rises, or it has dropped below the threshold level.
So is it as simple as that? Well, no, not really. You have to have a rough idea about how fast you will play to get the best out of it. Say you are a double bass drum pedal player and you play a lot of 16th notes on the bass drum(s). If you play at 120bpm, then each 16th note takes just over 31ms before the next one comes along. So if you don't play above 120bpm, you could comfortably set your reject time to 30ms and you wouldn't miss a beat.
If you play at (more realistically) 240bpm, then you would have to set your reject time to 15ms (if you were hyper accurate) or, say, 10ms to allow for 'drift' in timing, assuming you play a lot of 16th notes, but 16th notes at 240bpm is the stuff of heroes (or idiots, depending on your standpoint).
The same with toms – 16ths note at 240bpm and you should aim for a Reject Time of 15ms or less. But again, that is high on the scale of 'Help, my arms are melting' so more realistically, if you're in a function band and the fastest track you play is 180bpm (still pretty fast) you should be fine with a Reject Time of 22ms on all drums... except the snare.
On the Reject Time front, the snare is a complete pain. On one hand, you mostly play backbeats which are easy to trigger from, but we also play loads of ghost noters and buzzes, so its a bit of a triggering nightmare. This is where, in most cases, triggering off a snare is a compromise.
To get good triggering performance off a snare, it may be better to dampen the snare more than you usually would. This takes the processing power off the module, but it may spoil your acoustic snare sound.
The other option is to trigger only on the backbeats (raise the threshold to do this, and choose a velocity curve so that the back beats triggers gradually fade in, rather than suddenly go 'BANG'). This lets you keep your nice acoustic snare sound but doesn't trigger so noticeably on the ghost notes.
But there is a trick which I have been using for years (well, about 15, since doing a tour where everything was triggered off my acoustic kit) which can help. I call it the MoonGel trick, and its great if you are having a bit of a nightmare triggering your snare.
If you squash a small (½ or ¼) piece of Moongel (other dampening materials are available!) between the head and the sensor of the trigger, a very useful thing happens. Hopefully that small amount of Moongel wont change the snare sound TOO much, but what is does do is act like a natural noisegate – only definite hits on the head will be big enough to create a trigger signal. All other vibration in the head will be absorbed by the MoonGel or the angle of the waveform is slowed down so much that the module ignores it.
You will have to reset you Gain, Threshold and Curve setting but it can be a real 'Get Out Of Jail Free' lifesaver sometimes. A couple of manufacturers have tried similar things in the past, but the best thing about my suggestion is that you don't have to buy new triggers and most drummers have some Moongel kicking about somewhere.
Simon