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Live Faders - Can't determine scale...?
Posted: Sat Oct 14, 2006 11:11 pm
by Allison Redhead
Hello Abletons.
Here's a quick exchange from the forums at JazzMutant. I'm trying to get a Lemur to display the exact dB setting on an Ableton track. Seems it's not trivial. Hence:
Allison Redhead wrote:Hello!
After some downtime with a "Haunted Lemur" I'm back!
I'm still trying to get a setup that will show the correct dB figure for a fader in Ableton and put it into a text (monitor) element.
Anyone?
-Ali
axel wrote:good to see you back
It turns out to be a bit hard to reverse engineer the logarithmic scale Ableton uses to convert 7bit MIDI range to [-inf, +6dB]
This approximation doesn't suck too badly above 0dB, but goes way off when reaching low values :
20*log(x*127/108)*6/3.241
Maybe I'm missing something obvious here. An interesting thing to do would be to control two faders of two hosts from midi, and see if they appear to have the exact same scale.
Help!
Posted: Sun Oct 15, 2006 10:31 pm
by Allison Redhead
BUMP.
Posted: Sun Oct 15, 2006 11:28 pm
by longjohns
is there not a way to capture the sysex information, rather than performing a calculation based on the position of the MIDI controller?
dB values are sent out to a MCU unit when a fader is moved, for display on the controller
Posted: Sun Oct 15, 2006 11:35 pm
by Allison Redhead
longjohns wrote:is there not a way to capture the sysex information, rather than performing a calculation based on the position of the MIDI controller?
dB values are sent out to a MCU unit when a fader is moved, for display on the controller
The issue is that computing from the MIDI values is awfully hard. It's not self-evident what the formula is.
Posted: Mon Oct 16, 2006 5:10 am
by longjohns
sure, but what i'm asking is
if it is indeed possible to capture the sysex messages which are relating the dB levels
then why bother trying to convert the midi values at all
I don't know for sure if it's possible or not, but I suspect that it is... and I'm trying to encourage you to look into it!
Posted: Mon Oct 16, 2006 7:55 am
by hoffman2k
longjohns wrote:sure, but what i'm asking is
if it is indeed possible to capture the sysex messages which are relating the dB levels
then why bother trying to convert the midi values at all
I don't know for sure if it's possible or not, but I suspect that it is... and I'm trying to encourage you to look into it!
It's possible. But it's a pain in the arse to do.
For starters, you need to split the incoming sysex messages into 8...
Posted: Mon Oct 16, 2006 8:02 am
by Johnisfaster
are all of you speaking greek or what?
Posted: Mon Oct 16, 2006 11:44 am
by axou
longjohns wrote:sure, but what i'm asking is
if it is indeed possible to capture the sysex messages which are relating the dB levels
then why bother trying to convert the midi values at all
I don't know for sure if it's possible or not, but I suspect that it is... and I'm trying to encourage you to look into it!
The problem with this solution is that along with dB values, the host also sends text in the LCD sysex messages, and sometimes sends several values in the same message etc, + it won't send the dB if the host is in Device Edit mode, etc etc
There's an object on the Lemur that emulates a Mackie LCD display and shows exactly what the host wants it to. It would still be interesting to compute the dB value on the Lemur itself.
Posted: Mon Oct 16, 2006 2:21 pm
by longjohns
fair enough
Posted: Mon Oct 16, 2006 3:22 pm
by Audio Soundation
Johnisfaster wrote:are all of you speaking greek or what?
its just engineering.
Posted: Tue Oct 17, 2006 8:32 am
by Allison Redhead
Anyone?
Posted: Tue Oct 17, 2006 8:37 am
by hoffman2k
Reverse engineer it.
Set it to inf dB and assign a midi controller. Note down the results each time you move the controller up 1 value.
Probably the only way you're going to find the logic behind the scaling.
Posted: Thu Oct 19, 2006 2:32 am
by Allison Redhead
Bump? Anyone?