[sdiy] MIDI volume to volts formula

MTG grant at musictechnologiesgroup.com
Tue Jul 10 15:27:27 CEST 2018

Well it's a good way to capture the velocity output possibilities of a 
given synth.  There are some other applications out there, or I should 
say were, most are gone now. It seems we are archaeologists on a path 
that has been traveled before. This discussion appears to have come up 
on various forums before, including the histogram interrogation.

The DX7 has 5-bit, yes, sort of. It seems to generate the full 7-bit 
from the sub-CPU's timer and I think it uses that internally for sound 
generation. Then it's shifted right twice before being used for access 
to a 5-bit table that corresponds with the MIDI Out velocity.  I woudn't 
mind figuring out the histogram of that internal 7-bit value too.  
Changes to the mapping will affect the behaviour of two DX7's tied 
together, so that needs to be considered.

On 7/10/2018 3:36 AM, Tom Wiltshire wrote:
>> On 10 Jul 2018, at 10:35, Hugh Blemings <hugh at blemings.org> wrote:
>> Hi Brian, All,
>> On 10/7/18 16:34, rsdio at audiobanshee.com wrote:
>>> It took a month before I got started on a MIDI Velocity histogram app, but only a couple of hours to actually write it (thanks to CoreMIDI, etc).
>>> I’ve only done a quick test with an Ensoniq VFX set to the defaults, so I’ll need to spend more time with other keyboards as well as looking into the velocity curve settings options.
>>> With the VFX, I’m only seeing 45 unique velocity levels (not counting 0, of course). The VFX reaches up to velocity 127, as well as 126, 125, 124, and 123, but then there are gaps between the remaining velocity values at 120 and below.
>>> Based on your description, the DX7 only implemented 5-bit velocity instead of the full 7 bits.
>> Two questions come to mind on this;
>> Would you be happy to share the app ?
>> If so, does it make sense to build an export function and then dump the resultant data into (say) a Google Spreadsheet so that we can build up an archive of the histograms ?
>> I realise that without actual velocity measurements from the keyboard itself or timings from the contact closures the data only really gives general resolution/bit depth info, but might be interesting anyways ?
>> Just a thought :)
> Timings from contact closings is going to depend on the specific mechanics of a particular keyboard mechanism anyway, so might not be that general.
> T.

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