rev2-master-keyboard

The Prophet Rev2 is a polyphonic analog synthesizer, paired with a 5-octave keyboard, with modulation and pitch wheels, and inputs for expression and sustain pedals. For these reasons, it's a common scenario to use it to control other devices, via MIDI. However, since it wasn't designed to be used as master MIDI keyboard, it falls short in a variety of ways.

Using a Midihub, this project works around these limitations, so that the Rev2 can be used as a master MIDI keyboard.

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Features

• Split MIDI related to the Keyboard into its own MIDI channel, independent of the Synth's channel.
• Control the Keyboard's MIDI channel, Zones and other parameters through MIDI CC.
• Knobs operate as if Local control would be On, i.e. they control the Synth and also trigger MIDI messages.
• Zones
  • Split the Keyboard into zones A and B, independently of the Synth's layers.
  • Assign Zones to different MIDI channels, independently of the channels the Synth operates on.
  • Transpose each Zone independently, e.g. transpose Zone A by -2 octaves, and Zone B by +1 octave.
• Fixes Rev2 issues:
  • When Local Control is Off and Multimode is On, using the Program and Bank knobs now also changes Layer B's preset.

Usage

Once you have followed the Setup Instructions, you can think of the Rev2 as two independent devices: a Synth and a Keyboard. Both are accessible through Midihub's IN A and OUT A but on separate channels. The Synth operates on the channels you've configured during setup (1 and 2 by default), and the Keyboard operates on an assignable channel, from 1 to 16.

You set the Keyboard's channel through MIDI CC messages sent to IN A, on channel 16. To do this, you can use any device capable of sending MIDI CC, e.g. a computer, a MIDI sequencer, or a MIDI controller like the one in the picture above (Faderfox EC4). See Control Plane for a list of all parameters you can control.

The Keyboard outputs the following types of messages, on the assigned channel:

• Note On/Off
• Channel Pressure (aka Aftertouch)
• Pitch Bend
• Modulation Wheel (CC1)
• Expression Pedal (CC11)
• Sustain Pedal (CC64)

You can also optionally assign the Expression Controls (Channel Pressure, Pitch Bend, Modulation Wheel, Expression Pedal and Sustain Pedal) to a different channel than Note On/Off messages.

When you turn a knob in the Rev2, it is immediately reflected in the sound (as if Local Control would be On), and NRPN messages are sent through OUT A. You can also send clock, transport, NRPN or any other MIDI message to the Rev2, through IN A on the channels you've configured (1 and 2 by default).

Note that the Midhub keeps its memory across power cycles. If, for example, you set the Keyboard's MIDI channel to 7, then turn the Midihub off and back on, the Keyboard's MIDI channel will still be set to 7.

Zones

You can split the Keyboard into two Zones (A and B), which are unrelated and operate independently of the Synth's splits. In fact, the Rev2's feature of splitting the keyboard into two splits is no longer used, with Zones being implemented solely on the Midihub. This gives us the flexibility to, for example, change the octave of each Zone independently, a feature the Rev2 does not provide.

In practice, this means the Split A|B button on the device's panel continues to work as expected in what concerns the Synth's layers, but has no effect whatsoever on the keyboard. When the Split A|B button is lit, each layer continues to be addressable through IN A, on the channels you've previously configured (assuming Multimode is On).

You can configure Zones through the Control Plane.

On an initialized patch, only zone A is enabled, and it occupies the totality of the keyboard. Once zone B is enabled, it occupies the right side of the keyboard, starting at the 3rd C note. Zone B's Start Key (i.e. the split point), can also be configured through the Control Plane.

Caveats

NRPN

The Rev2 must be set to send and receive NRPN instead of CC, i.e. both the MIDI Param Send and MIDI Param Rcv settings must be set to NRPN. See here for why this is the case.

This means, the Synth (OUT A) will output NRPN, and will only accept NRPN as input (IN A). This can be limiting when using the Rev2 with other gear, since most do not support NRPN. For example, you won't be able to automate the filter cutoff frequency with an external sequencer that does not support NRPN, which is the case with many sequencers.

However, there are plans to add NRPN-to-CC conversion to the Midihub, which would likely allow this limitation to be addressed.

Control Plane

You can control various parameters of the Midihub's patch through MIDI CC messages sent to IN A, on channel 16.

• Zone A MIDI Channel
• Zone B MIDI Channel
• Zone A Octave
• Zone B Octave
• Zone B Start Key
• Zone B Enable/Disable
• Expression Controls MIDI Channel
• Request CC Dump

CC1: Zone A MIDI Channel

Set the MIDI Channel of messages produced by Zone A of the Keyboard.

This does not control the channel of the Synth's Layer A, that's still configurable through the Rev2's Global Settings.

CC1 Value	Zone A MIDI Channel
0, 1	1	default
2	2
3	3
...	...
16 - 127	16

CC2: Zone B MIDI Channel

Set the MIDI Channel of messages produced by Zone B of the Keyboard.

This does not control the channel of the Synth's Layer B, that's still configurable through the Rev2's Global Settings.

CC2 Value	Zone B MIDI Channel
0, 1	1
2	2	default
3	3
...	...
16 - 127	16

CC3: Zone A Octave

Transpose Zone A up or down N octaves.

First-key note is the note produced by the 1st key on the keyboard.

CC3 Value	Zone A Octave	First-key Note
0	-3	C-2
1	-2	C-1
2	-1	C0
3	+0	C1	default
4	+1	C2
5	+2	C3
6	+3	C4
7 - 127	+4	C5

CC4: Zone B Octave

Transpose Zone B up or down N octaves.

First-key note is the note produced by the 1st key on the keyboard.

CC4 Value	Zone B Octave	First-key Note
0	-3	C-2
1	-2	C-1
2	-1	C0
3	+0	C1	default
4	+1	C2
5	+2	C3
6	+3	C4
7 - 127	+4	C5

CC5: Zone B Start Key

Set the key on the keyboard from which Zone B starts, inclusively.

In other words, the split point between Zones A and B.

CC5 Value	Zone B Start Key
0, 1	1st C	Zone B occupies entire keyboard
2	2nd C
3	3rd C	default
4	4th C
5 - 127	5th C

CC6: Zone B Enable/Disable

Enable or disable Zone B.

When disabled, all keys on the keyboard are assigned to Zone A.

CC6 Value	Zone B status
0	Zone B Disabled	default
1 - 127	Zone B Enabled

CC7: Expression Controls MIDI channel

Set the MIDI Channel of Channel Pressure, Modwheel, Pitchbend, Expression Pedal and Sustain Pedal.

CC7 Value	Expression Controls MIDI Channel
0	Same channel as Zone A notes	default
1	1
2	2
3	3
...	...
16 - 127	16

CC127: Request CC Dump

Requests a dump of all CCs.

Upon receiving this message, for each of the CCs above (CC1, CC2, CC3, etc), one message will be output to OUT A, on channel 16, containing the current value of the respective CC. This is useful so an external MIDI controller can be "refreshed" to the internal state of the Midihub.

CC127 Value	CC Dump
0 - 127	All CCs are dumped

Rev2 limitations

This section lists some of Rev2's limitations, some of which this project addresses.

No hybrid Local Control mode

It's not possible to have the knobs control the device, while the keyboard just sends MIDI. If it would, this project would probably not need to exist, or its scope would be significantly reduced.

LFO and other parameters not sent in CC mode

With Local Control set to Off and MIDI Param Send set to CC, for many of the Rev2's parameters, no MIDI message is triggered when the parameter changes. This is because there are more than 127 parameters in the Rev2. Setting MIDI Param Send to NRPN fixes this issue.

Program Change in Multimode

With Local Control set to Off, and Multimode set to On, Program Change messages triggered by the Program and Bank knobs are only sent to Layer A's MIDI channel, i.e. they aren't duplicated to Layer B's MIDI channel. In a setting where these messages are re-routed back to the Rev2, this causes Layer A's Program to change, while Layer B's Program remains unchanged.

Contributing

If you use this project and have any issues with it, or have any kind of feedback, please consider opening an issue.