Highly Liquid Forum facebook twitter google plus rss feed
Old 12-23-2015, 11:29 PM
shirsch shirsch is offline
Junior Member
Join Date: Sep 2015
Posts: 2
Default Logarithmic response to analog input?

I have a feature request: Would it be possible for the MIDI CPU to produce a log response to input voltage change in software? Doesn't have to be instrumentation grade. A lookup table and/or simple-minded interpolation is close enough.

My immediate issue is the need to piggyback analog control on the mag pickup volume pot in my guitar. Most CC analog controls in my Roland / Boss products expect a linear voltage ramp. Since it's relatively easy to get ganged audio-taper pots a log function would be handy here!

I briefly looked into building an op amp based log amplifier circuit, but it starts getting complex rather quickly and requires calibration. Better done in software if at all possible.

Bump: Hello? Is this on?

Update: I found a rather elusive bit of PIC assembly code for fast 8-bit logarithms. Let me know if you want a copy?

Last edited by shirsch; 12-28-2015 at 06:55 PM. Reason: No response - not seen?
Reply With Quote
Old 01-06-2016, 12:00 PM
shirsch shirsch is offline
Junior Member
Join Date: Sep 2015
Posts: 2

Bump... Would appreciate some sort of response to my original post - thanks.
Reply With Quote
Old 01-08-2016, 02:33 AM
Synthetech's Avatar
Synthetech Synthetech is offline
Join Date: May 2012
Location: USA
Posts: 711


sorry for the lack of response.

I doubt any changes to the MIDI CPU's firmware can be done to meet your needs.
It would require the designer/author, John S., to do it and I think he may be deep into other projects right now.

I'd suggest PM'ing him and ask him directly.

this link may take you to his profile, just click "Send Message" below his name to send off a PM


another thought is to check into using an Arduino and the MIDI Library to custom build a device to translate your voltage controls for you.. something you'd have to get support for elsewhere, I'm afraid.

Last edited by Synthetech; 01-08-2016 at 03:01 AM.
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

All times are GMT. The time now is 05:28 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.