Midi Keyboards Aftertouch – Channel vs Polyphonic

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Buying a Midi Keyboard with Aftertouch? Not sure what it is or what the difference is between Channel and Polyphonic Aftertouch? Let’s find out!

In today’s article we are going to explore Midi and figure out what Midi Keyboards Aftertouch is, and what is the difference between Channel and Polyphonic Aftertouch. To do this we will start with refreshing our brains on what is Midi and the history behind it. Then use this information to build a picture of Aftertouch. Finally, we will see what the right hands can do with Aftertouch and check out a few of the Midi Keyboards that offer Aftertouch.

 

What is Midi


Musical Instrument Digital Interface (Midi) is a key part in understanding what Aftertouch is all about, since Midi is the method through which the information is sent. Let’s have a quick look at what is Midi and how it works.

Midi a Brief History

Midi as we know it was first discussed in 1982 with a few of the key players in the synthesizer market at the time (Yamaha, Roland, etc). Development of the technology took place over this time and was first demonstrated at the NAMM conference in 1983 where two synthesizers (Sequential Prophet-600, Roland JP6) were connected together and one controlled the other. The Midi technology has since been enhanced by the custodians, The Midi Manufacturers Association (MMA) ever since. Interestingly even though there have been enhancements the technology is still officially on version 1.0.

The most recent update to the technology has been the adoption of the USB standard as a means of Midi information/data transport. The USB standard, in particular USB 2.0 has alleviated the original Midi Bottleneck of 32 kbps with the ability to send 480 Mbps along with power over the same connection. This has resulted in many Midi Keyboards these days, needing only a single USB connection to send data and receive power.

Check out on of the pioneers of Midi in the video below!


What is Midi Data

You can think of Midi data as bunch of instructions that are then sent (very quickly) to a synthesizer or instrument to carry out. For example if you were to hit the middle C note hard and hold it, this would result in the following messages being sent:

  • Key On
  • Middle C Note
  • Velocity the key was hit with (Hard)
  • How hard you are pressing on the key
  • Tempo you are playing at
  • Panning (middle-ish)
  • Modulations (none for our example)
  • Volume – not to be confused with Velocity, think of this message as “what volume the speakers should be at”

As you can see there is a lot going on here even for just a single pressed key. If you are familiar with Midi already you may have come across the different types of messages like Note, Control Change (CC), Program Change etc. These are all type of midi events that wrap up the above messages in different ways. For example a Note event can be used when you hit a key and a CC event can be used when you move a fader or turn and encoder. However, the great thing about Midi is that it is flexible and you can program any message to any action you can think of. Your only limitation is the abilities of your hardware controller.

A great example of this flexibility is the Roli Seaboard Rise which you can learn more about here, and we discuss it later in this article too.

 

What is Aftertouch


So now that we have an (better) understanding of what Midi is, let’s have a look first at Channel Aftertouch. If you remember back to the example above of hitting a not and holding it, and the different midi messages that were sent, Aftertouch comes in at the 4th point down (How hard you are pressing on the key).

Aftertouch

So what does this mean? Well, as you hold a note (middle C for example) you can change how hard you press down. This pressure information can be sent to a synth or other instrument and interpreted to do whatever you like. For example, you can have this control a filter parameter so that when you press hard the filter is not/barely working and as you release pressure, the signal is filtered.


Aftertouch vs Velocity

Take care not to confuse Aftertouch with Velocity since, yes, they are very similar in that you could say they are a measure of how hard you press a key, but, they are different. Velocity is a single measure of how hard you hit the key initially, so the very first time the key makes ‘electrical contact’ (not a real term but hopefully it makes sense), how hard did it hit. In contrast, Aftertouch is a continuous measure of pressure as you hold the key down, until you break the ‘electrical contact’ of the key.

 

Channel vs Polyphonic Aftertouch


You may often see on Midi controller specs that ‘YES’ Aftertouch is enabled But take care to note what kind of Aftertouch the manufacturer is talking about as often this detail will be buried in the manual. So that you know what to look for, let’s compare the different types of Aftertouch that is common (or not so common) among the Midi controllers of today.

Channel/Monophonic

Taking into account what we know about Aftertouch already, Channel or Monophonic refers to the amount of Aftertouch information that can be sent at a time. In this case it is just a single channel of information… so what does that mean?

Let’s say you are play a chord on a keyboard and it is made up of three notes, with Channel Aftertouch all you need to do is vary the pressure of one of the keys, and this will send a single Aftertouch message telling the synth/instrument to change the mapped parameter for all keys that are held down.


Polyphonic

Polyphonic on the other hand (as the name implies) can send multiple Aftertouch messages, one for each note. So using the same example as above, this item when a chord is held down and a single key has the pressure on it varied, just this note will have the mapped parameter changed and the others will not. In the same way if you were to vary the pressure on all three keys, this would in turn send three Aftertouch messages each independent of the other.

 

Aftertouch enabled Keyboards


Now that we know what Aftertouch is and the differences between Channel and Polyphonic, let’s have a look at a few of the keyboards that offer this functionality.

Channel Aftertouch enabled

Studiologic SL88/73

This is an 88/73 key Hammer action Midi Controller with three XY joysticks that you can map to any function you like. It has a super simple design and not a bad price tag considering its competitors.

Check out the pricing here: SL88


Arturia Keystep

Here is a small form factor controller with a lot of functionality and generous IO connectivity. This is a great little keyboard and combined with after touch makes it perfect for recording solos of synths and even sampled instruments.

Check out the pricing here: Keystep


Polyphonic Aftertouch Enabled

Roland A-80

A tough one to come by these days with your best bet being eBay. However, this is one of the best Polyphonic Aftertouch keyboards around so if you see one for sale snap it up quick before someone else does!


Roli Seaboard Rise

We did a review on the Seaboard Rise a few weeks back that you can check out here. I wouldn’t say that is exactly is Polyphonic Aftertouch enabled, but it is. Also, what it is, is an awesome example of the flexibility of Midi.

Check out pricing here: Rise 49

 

Why do we need Aftertouch


At this point you may be thinking, “OK I get what AFtertouch is now, but what can you do with it?” So rather than try to explain it, here is a video we posted in the Roli Seaboard Rise review that I think best answers that question.

If you are still unsure then let me tell you, AFtertouch adds and other layer of expression to playing. Think of it like vibrato on a violin!

 

The Wrap-up


Right then, so now we know about Midi Aftertouch and what it can do and the different types manufacturers are building into their hardware.

Aftertouch has actually been around since the early days of synthesizers, but became less popular over time. This was due to its lack of popularity since most consumers associate a keyboard with a piano which does not have any sort of Aftertouch characteristic. Polyphonic Aftertouch keyboards these days (if you can find them) also carry a higher price tag than normal, and then if you are using a computer you may have trouble finding virtual instruments that support it anyway.

For me polyphonic Aftertouch is not a necessity but I sure wouldn’t mind trying it out for a while. The main reason I don’t feel I need it is that I have become accustomed to working with faders that are either part of the Keyboard or as a separate controller. I play the notes with my left hand and control [removed]faders) with the other. For now this works just fine for me, and I can at any time remap the faders to control something else.

So hopefully that was helpful to you in understanding Aftertouch and Midi for the next time you are looking to buy a Midi Keyboard. Let me know if you have any other questions in the comments below and if you liked this don’t forget to hit that like button!

Wondering what to read next? Why don’t you take a look at one of our Midi Keyboard reviews here, or check out the latest music production industry news here.
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6 thoughts on “Midi Keyboards Aftertouch – Channel vs Polyphonic”

  1. Very interesting topic. I stayed on the page we get to with the link you provided. As I said to someone else pictures are nice. I usually let my eyes relax on them while I am scrolling donw the webpage . I am not sure if you are selling

    Polyphonic Aftertouch Enabled or why they are on your webpage. Now I wonder why i love technical knowledge so much. You provided interesting knowledge on after touch. Something I have never heard of. My brother is musician working with DAWs . I have some musical experience myself too . Thanks

    All in all I think you msut continue the same way you started. Lets see how you do with this. Very enjoyable reading

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  2. Hey Tim,
    What an informative read! I knew nothing about the subject before starting. But you guided me expertly through the technical discussion, and now I feel informed about what channel and polyphonic Aftertouch can do. Thanks for sharing.
    Wendy

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