Live Faders - Can't determine scale...?

Allison Redhead · Post by **Allison Redhead** » Sat Oct 14, 2006 11:11 pm

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!

Allison Redhead · Post by **Allison Redhead** » Sun Oct 15, 2006 10:31 pm

BUMP.

longjohns · Post by **longjohns** » Sun Oct 15, 2006 11:28 pm

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

Allison Redhead · Post by **Allison Redhead** » Sun Oct 15, 2006 11:35 pm

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.

longjohns · Post by **longjohns** » Mon Oct 16, 2006 5:10 am

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!

hoffman2k · Post by **hoffman2k** » Mon Oct 16, 2006 7:55 am

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...

Johnisfaster · Post by **Johnisfaster** » Mon Oct 16, 2006 8:02 am

are all of you speaking greek or what?

axou · Post by **axou** » Mon Oct 16, 2006 11:44 am

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.

longjohns · Post by **longjohns** » Mon Oct 16, 2006 2:21 pm

fair enough

Audio Soundation · Post by **Audio Soundation** » Mon Oct 16, 2006 3:22 pm

Johnisfaster wrote:are all of you speaking greek or what?

its just engineering.

Allison Redhead · Post by **Allison Redhead** » Tue Oct 17, 2006 8:32 am

Anyone?

hoffman2k · Post by **hoffman2k** » Tue Oct 17, 2006 8:37 am

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.

Allison Redhead · Post by **Allison Redhead** » Thu Oct 19, 2006 2:32 am

Bump? Anyone?