Microsoft GS Wavetable Synth (“MSGS”) Supported Events
- Updated 2023-03-25

Ah, Microsoft GS Wavetable Synth. The default MIDI driver that comes with every version of Windows since Windows 98. But this isn't any old General MIDI synthesizer. It supports Roland's GS extension—later made into (significant parts of) GM level 2, because I guess Roland are the big shots of the industry. You'd think the “GS” in its name would make it obvious.

It is known to be very limited, basic and dry sounding. At the time of creation (around 1996 or so), some of these limitations could be by necessity. It had to be small so as not to take too much space, and it had to be performant while delivering pretty good sound. Nowadays, it's been mostly derided. Even Microsoft left this thing rotting, probably because “nobody is playing MIDI files anymore”.

Its lo-fi and crunchy vibe may sound like a mockery of the legendary Roland SC-55 samples that it's based on, and not to mention it's very easy to clip this thing to h*ck. But… if you know what you're doing, you can make it sound cool, or even push it to its absolute limits.

Sadly, its ubiquity (piggybacking off of Windows') caused it to be known as “the sound” of MIDI, despite that MIDI (as a protocol) inherently can take on many different sounds. I do think this warps what people (other than electronic musicians) think of MIDI as a general.

In any case, this document will attempt to explain what events this familiar software synth can handle, since existing documentation on this thing is sparse. It's best to assume that events not described here aren't processed by this synth.

Numbers denoted like FF represent a hexadecimal number. Fx means F0 plus x, where x is a variable number from 0-15 (0 to F).

GENERAL NOTE: Roland's GS standard has the concept of parts as separate from MIDI channels. There are 16 of them, and by default, these match their respective MIDI channels (Part 1 maps to Ch.1, Part 2 maps to Ch.2, and so on).

Part IDs (which marks their location in a GS device's memory) are mapped in a weird way. Part 10 has ID 0. Parts 11 to 16 are assigned the IDs 10 - 15, while the rest has IDs matching their part numbers (e.g. Part 1 has ID 1).

Messages #

Note off (8x) and note on (9x): The most basic MIDI event.
Control change (Bx): See the list of supported CCs.
Program change (Cx): For changing the currently playing instrument of a part.
Pitch bend (Ex): For twangs and the like.

Control changes (CC) #

For this section, CC numbers will be given in decimal and will be represented as regular text.

Bank select (MSB: 0, LSB: 32)

Sets the bank for the next program change. This allows the use for variations on instrument sounds. For example, patch 81 is a square wave lead, but setting the bank MSB to 1 will produce as pure as approximation of a 50% square wave as possible. Setting it to 8 will give you a sine wave instead. You can refer to this list for a short description of what variations are available.

Keep in mind that setting this CC after a program change will not have any effect! In addition, this will only work after the GS Reset SysEx has been sent. Some software such as vanBasco's Karaoke Player can do this automatically, however.

RPN select (MSB: 101, LSB: 100)

Sets the RPN to be affected by the Data entry CC. See the supported RPN list.

NRPN select (MSB: 99, LSB: 98)

Normally sets NRPN to be affected by the Data entry CC. In MSGS however, no NRPNs are supported, leaving this effectively useless.

That's not to say it doesn't do anything, however. If this CC is encountered, MSGS always sets it to 3FFF, the RPN reset ID.

Data entry (MSB: 6, LSB: 38)

Sets the currently selected RPN or NRPN to the specified value.

Modulation wheel (MSB: 1, ~~LSB: 33~~)

Sets an automatic vibrato effect, set to a rate of about 5 Hz. Its equivalent LSB CC is ignored.

Volume (7)

Sets the current part's overall volume level (0–127).

Pan (10)

Sets the current part's panning balance (0 = hard left, 64 = centered, 127 = hard right).

Expression (11)

Modifies the part's volume continuously. Useful for things like crescendos.

Hold/sustain pedal (64)

When set, this sustains currently-playing notes until it is reset.

All sound off (120)

Kills all sound indiscriminately. Can also be used as a "panic" button.

All controllers off (121)

Resets the state of all controllers. Specifically:

Volume = 100 (about -4 dB)
Pan = 64 (center)
Expression = 127 (max)
Volume = 2000 (2 semitones)
Mod Wheel = 0 (off)

All notes off (123)

Kills all notes. If the Hold/Sustain Pedal is enabled, it waits until that particular CC is disabled first.

Mono mode (126)

Kills all notes and enables Mono mode for this particular part.

Poly mode (127)

Kills all notes and enables Poly mode for this particular part.

As is often noted, MSGS doesn't support effect CCs such as 91 (reverb send), 93 (chorus send), and 94 (delay send). Neither does it support ADSR manipulation CCs like 72 (release), 73 (attack) and 75 (decay; but this is a GM2 CC).

Personally I want the ADSR ones, but alas, none to be found. Wish it did. (“You already have one: it's called VirtualMidiSynth!”)

There's another option, however. Edirol VSC 1.60 + VST SysEx patch + VSTi Driver may be the closest direct substitute. Given the very similar sound (it was made around the time of MSGS after all, around 2001) and being actually able to read the ADSR CCs I wanted, it's like a better version of MSGS that almost retains the lo-fi-ness but has more support for effects.

Registered Parameter Numbers #

RPN numbers are given as xxyy, where xx is the RPN number's MSB, and yy is its LSB.

Pitch bend (0000): Range of bending for the Pitch Bend message. Upon data entry, only MSB is taken into account, while LSB is ignored. In this case, this means only the range in semitones are considered.
Fine tune (0001): Transposes the entire part by some amount of cents relative to 2000 (= A 440Hz) Both LSB and MSB are accepted on data entry.
Coarse tune (0002): Transposes the entire part by some amount of semitones relative to MSB = 40 (= A 440Hz). Upon data entry, only MSB is taken into account, while LSB is ignored.

System Exclusives (SysEx) #

This section will use the following convention:

Let SYSEX, where SYSEX is an array containing the entire SysEx string as a series of 8-bit numbers from start (marked with F0) to finish (marked with F7). The array starts at 0, so SYSEX[0] = F0.

Array slices are written in Python's slice notation, so SYSEX[:3] == SYSEX[0:3] == {SYSEX[0], SYSEX[1], SYSEX[2]}.

Example: SYSEX = F0 41 10 42 12 40 00 7F 00 41 F7

SYSEX[0]: F0
SYSEX[1:3]: 41 10
SYSEX[3:7]: 42 12 40 00
and so on…

In general:

SYSEX must have a minimum length of 6 bytes.
SYSEX[2] normally contains the device or sysex channel ID. It is ignored in MSGS.

SYSEX[1] contains a vendor ID, of which only three are recognized:

7E for Universal non-realtime
7F for Universal realtime
41 for Roland

Universal non-realtime #

Only GM Reset is supported by this vendor ID:

SYSEX[3] = 09
GM Reset. Specifically:
- Reset all parts data.
- Disable GS.
- Reset fine tune.
- Restore default scale tuning (and coarse tuning).
- Set polyphonic mode.
- Restore drums to Ch.10 only.
- Set master volume to 0.
Continuing from above, SYSEX[4] = 01.
This enables strict GM mode. However, whichever value is found in here doesn't seem to actually matter, and will set GM mode regardless.

Universal realtime #

Only Set Master Volume is supported by this vendor ID:

SYSEX[3:7] = 04 01 ?? xx
Set Master Volume where xx is the volume. ?? is ignored.

Roland #

For this vendor ID:

SYSEX must have a minimum length of 11 bytes. This includes the checksum byte.
However, although the checksum byte must be present to fulfill the 11 bytes minimum, it is not actually checked. Keep in mind that setting an invalid checksum may render it not working on proper GS hardware.
SYSEX[3:5] must be 42 12 (pick GS model ID, send the following SysEx data).

SYSEX[5:8] contains the GS address to be modified (and hence the operation to be done), and will be one of the following:

40 00 7F = GS Reset.
This switches the synth to GS-compatible mode, and must be sent first in order to use the operations below, as well as the bank select CC. Any data following this reset address won't have any effect.
40 1x 02 = Set MIDI Channel for This Part.
x is the part ID.
A single byte yy follows, and is the MIDI channel to map that part to. I believe this is expressed normally, with 00 specifying the first MIDI channel and 0F specifying the last one.
40 1x 15 = Set as Drum Channel.
x is the part ID.
A single byte yy follows, and is either 00 (for False) or 01 (for True).
40 1x 40 = Scale Tuning.
x is the part ID.
Directly following this is the tuning adjustment for 12 notes on the scale, made up of 7-bit numbers where 00 is an adjustment of -64. If tuning data is for less than 12 notes, it can be terminated by inserting an 80.

Additional Information #

The maximum number of MIDI events it can handle per second is 1000.
Maximum polyphony appears to be 32 voices, although some say it's 64 in Windows XP. "Certain sources" say this appears to be actually 48 (+6 overload voices). Whatever the case, it seems noticeably reduced by now.
A quirk of the synth is that one note played in quick succession will immediately kill the previous instance of that note, say a snare drum with velocity 127 and then another with velocity 59—the lower velocity snare drum will cut off the higher velocity one including envelopes.
This effect may be used for echo effects or a quick release, however this may not work as expected on more advanced synths.
The lack of customization for CC 1 (Mod Wheel) may drive you to use the pitch wheel messages. In which case, ensure that the ranges are defined by setting RPN 0000 appropriately.
MSGS prioritizes notes playing at lower channel numbers than higher ones, for example Ch.1 is prioritized over Ch.2. If you find yourself bumping up against the polyphony limit, consider giving your channel layout a look.