Handling Rejection - Rejection Time

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;

Screen Shot 2018-04-27 at 15.56.07.png

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.




07 Polyphony

Okay, so here's our next subject – polyphony.


So what on earth is polyphony? Well, it comes from two Greek words, 'poly' meaning 'many', and, 'phony', meaning notes, and for us drummers it just means how many notes can your drum module play at the same time.

If you think about it, your acoustic drum kit has unlimited polyphony. You can hit every drum and cymbal as fast as you want, and as many times as you want, and nothing strange will happen - you'll hear everything and everything will ring until all the vibrations of stopped. The same cannot be said for a electronic drum kit.

All electronic drum kits have a processor of some sorts controlling the playback of sounds, all your settings and parameters, and everything else associated with making it sound vaguely like a drum kit. Now all processors have a limit to how much they can process at the same time. On electronic drum kits, processing limits regulates how many notes your drum kit can play at the same time without there being any problems.

So maybe your electronic drum kit has 64 notes of polyphony. That means you can play 64 different hits and each one of them will sustain for as long as it is required to do, but as soon as you play a 65th note, (usually) the very first note that you played will stop (this is called 'note stealing'). In most situations, this really isn't a problem as by the time you get to note 65, the first note you played will have died away and cannot be heard.

However, if that first night you played was a drum loop and it's looping round and round, and you are busily playing over the top with long sounds, then you may be in for a surprise. If your first note was the loop, and notes 2 - 64 are long samples (such as cymbals and ringy toms) and you hit another note on top there is a good chance that your lovely, grooving, drum loop will stop. This could be quite embarrassing if it happens in front of a large audience.

Of course, this doesn't often happen as we don't generally play 64 notes of long ringing sounds such as ride cymbals (or do we?). However, how long does it REALLY take to play 64 notes? Well, if I play a nice, clean, fast buzz roll, then I can hit 64 notes in a little under 2¼ seconds (I just checked with a Keith McMillen Bop Pad into Garageband if you want to know). And that is without using long samples. So if I were to start a gig with a drum loop and then do a buzz roll, I'd probably be in trouble.

So what, you're thinking, I've never heard of this happening. Well, last summer I had a call from a friend/client of mine who had this exact problem. He was triggering a backing track off a (well known) sample pad device, and playing a groove over the top on the same device. Normally he played a simple eighth note groove, but he was doing a festival and was enjoying himself in front of a lot of people, so he flung in a few extra 16th note hi hat bursts that he didn't usually play... and you can guess the rest.

So I looked into why this had happened and to my massive surprise, the device had a polyphony of 'around 20'. Which means if you trigger a backing track and do less than a seconds buzz roll, then you might (probably) come unstuck.

But what if you don't trigger backing tracks and loops off your kit? Well, you can still have issues. If you've been reading the previous articles (and if not, WHY not? Grrr...!) then a bell might be ringing in the back of your mind somewhere that this cropped up before.

On the article about Threshold (the level below which pad hits are ignored), then I mentioned how having your threshold set wrongly could be using causing your kit to sound strange. This is because, if the threshold is set too low, then vibration (through the floor) and crosstalk (from other pads) could be triggering sounds (often so quietly that they cant be heard) causing your module to lose half or more of its polyphony. This could be making your cymbals stop unrealistically or other drums or pads to 'choke' or stop for no obvious reason.

As an example, if your thresholds are set way too low, then a single ride cymbal hit could also be triggering your crash pad and the three toms (because of the vibration through the rack), instantly lowering your polyphony from 64 (say) to 12 (roughly). So less than half a second of buzz roll and your module will be 'note stealing'.

Also, if your 'Reject Time' settings are wrong, then you might be eating into your polyphony as well. We'll look at Reject Time (also known as Mask Time) very soon. But if you have ever been playing constantly on a pad and then suddenly one note is much quieter than the rest (it often seems to happen when triggering big, long tom sounds on wobbly pads), then you possibly need to look at your Reject Time as they might be allowing the vibrations of the pad to steal even more notes than just your playing.

So what can we do? Surely it seems pretty hopeless – our electronics are out to get us!

Well, not really. The reality of it is that the major manufacturers have develop some pretty clever ways of disguising polyphony without it (hopefully) affecting us. These are things like not stealing the first note played but stealing the quietest note playing or the quieter of two similar sounding instruments (after all, can you seriously tell how many times a tom has been hit by only listening to the ringing of the head?). Generally this works fine, but on some occasions things just happen and you wonder why everything has stopped.

What you CAN do is buy gear that has better polyphony than other similar products. That way, at least you'll be able to to trigger a backing track AND demonstrate your sexy buzz roll to the audience of 150,000 at Glastonbury without unnecessary embarrassment.

06 Curvaceous Dynamics? Erm... No mate... Dynamic Curves!

06 Curvaceous Dynamics? Erm... No mate... Dynamic Curves!

Okay, so here's another subject which might initially seem rather boring and inconsequential, but is actually very important for the feel (not sound, importantly) of your electronic kit.

So what we actually mean by a dynamic curve (or velocity curve - same thing)?

Well, if you think about playing an acoustic drum, when you hit quietly, the drum responds quietly too. When you hit hard, the drum is loud. Simple and obvious.

05 Over The Threshold

05 Over The Threshold

I know I mentioned that we'd look at Velocity Curves this month but having had a think about it, it would make much more sense to look at those interestingly named Thresholds.

Thresholds? Ok, so you've probably seen that in your module (although it may be disguised with a different name) but it is actually MUCH more important that most people realise and can get you out of trouble very easily.

04 No pain, no gain, and no edrums

04 No pain, no gain, and no edrums

Well, that's a weird thing to be writing a blog about surely? Gain? Are you sure?

Absolutely. Its one of the most misunderstood things when it comes to electronic drums. Get it wrong and your pads act like switches – hit them and they make a noise at one level. Get it correct and you suddenly have a dynamic, sensitive instrument that begs to be played and is genuinely enjoyable to use.

01 In the beginning...

01 In the beginning...

For most drummers, electronics are a bit of a (as we say in the UK) 'Marmite' situation – you either love them or hate them. I meet loads of drummers who 'hate' electronics (and I use the word advisedly), and I meet just as many (if not more) who cant imagine life without them, and would probably say they 'love' them. Those who don't like them feel that electronics aren't real drums, aren't 'proper' and I can appreciate that and agree to a point – they aren't a replacement for acoustic drums.