Now your average SysEx message will look something like this:

F0 41 10 16 12 04 00 25 32 25 F7

In the spirit of 'one I prepared earlier' I can now tell you that when this message is sent to a Roland D-110 it will magically change the TVF Cutoff Frequency in Partial #1 of Part #1 on that machine to a value of 50, don't worry too much about the synths architecture as we are only demonstrating that something can be edited on the fly with SysEx. So lets break down what each of the 11 sections in the message actually mean.

Remember we said that SysEx is reflected in hexadecimal so we have 11 pieces of hex that are in fact 11 numbers of 0-255. The numbers themselves are less important in the context of the most important resource that you will require, which is the machines MIDI Implementation Chart and in particular its detailed addendum. This contains an 'address map' of every parameter that can be modified plus a whole bunch of other stuff such as how to do bulk dumps or transfers etc.

Sections 1, 2 and 11 are part of the MIDI spec and cannot be altered, these sections basically say 'I am a SysEx message and this is where I start and end'. Section 2 is a little more specific as it refers to the Manufacturer, in this case Roland. Section 3 is the Device ID which you will definitely need to get from your synth manual. In the case of the D-110 it is stated to be 17 (10h) and it's worth noting that Device ID's can generally be modified on the synth in the circumstance where you have two of the same model and you want one to ignore the message but not the other.

The next section is the Model ID (again refer to your manual) followed by either 11h or 12h to tell the synth whether we are sending info (12h) or asking for info to be sent back to the caller (11h). 11h messages are a whole other subject area, but only if you are really, really interested.

Section 6, 7 and 8 is where it gets interesting. Remember we said we wanted to alter the TVF Cutoff Frequency for a particular filter block on the synth. We send 3 bytes of data which are the hexadecimal sum of a particular base address and any required address offsets determined from our MIDI Implementation spec: 

04 00 00 - start address of Part #1 (Tone Temporary Area)

00 00 0E - offset address of Partial #1

00 17 - offset address of TVF Cutoff

The hexadecimal sum of all the above becomes 04 00 25. Section 9 represents the value we want the parameter to be modified to i.e. 50, which becomes 32h. Section 10 contains a checksum (not found on all synths) that is used to check message integrity and in this case it is calculated by the using the integer sum of sections 6 thru 9 in the following formula:

04 00 25 32 = 4 + 0 + 37 + 50 = 91 (integer sum)

then: 128 - (91 MODULUS 128) = 37 = 25h

Basically checksums can be tedious because for every value change a new checksum has to be calculated, which is why we do it in software!! Now the best way to test this is to use the excellent MidiOX utility (http://www.midiox.com/):

Now while I said before that we didn't care too much about what was sending the message let me give you a sneak peek as to how easily something very contemporary can integrate with our 25 year old D-110 (or similar) with no programming. In this case with Max4Live in Ableton using SysEx, which basically means editing can be done directly within the Live project and its controls can be mapped to other external controllers with knobs and sliders. It just gets better and better, another blog for another day.

ED NOTE: The D110 also had the ability to send a patch dump of the current setup as SysEX - very handy for storing the setup as a burst of data on a spare sequencer track and avoiding the need to say everything in memory.

Jason Durbin (aka Lagrange Audio) has been a synth and music tech enthusiast for 30 years since getting his hands on his first synth in 1983 at the tender age of 16. He hasn't earned a single Aussie dollar from music but the journey has been nothing short of incredible and he has met and interacted with some amazing people along the way. Jason is a true enthusiast doing it for nothing more than the pure love of it.