Marc Lavallée wrote:
Le 22 Mai 2005 05:14, IOhannes m zmölnig a écrit :
For those not using MIDI (which I believe is the case of most PD users), midi-dB is not that intuitive... And I don't see any reference about
hmm: i guess a lot of pd-users have no idea about technical dB too. so for them it should be just an abstract "unit", with 100 ("%" ??) being unity gain. i (normally) do not use MIDI and i don't have problems with it; however, i agree that it is confusing, especially if you have some knowledge about technical dB, and try to figure out whether to use "real" dB, "midi" dB or rms.
midi-dB in Miller's book. I can believe that midi-dB is handy and make sense, but I used MIDI and I don't understand your explanation (and the conversion pseudo code).
the pseudo code says: MIDIdB == dBfs + 100 that is all. the only thing that complicates the pseudo-code was, that i tried to express that "0" midi-dB (which is "-100" dBfs) is set to 0.0 rms (which is "-infinity" dBfs) by definition!
If 128 values are used to control a 0-100 dB range, it means that the midi-dB resolution is 0.78 dB. For 16 bits audio, the range is 0-96 dB, so the midi-dB resolution is 0.75. For 24 bits audio, the range is 0-144 dB, so the midi-dB resolution is 1.125 dB. Is that correct?
WHY ?
dB is a relative measure. +1dBfs == +1dB(midi) == +1dB(16bit) == +1dB(32bit) == ~ *1.12 (rms)
128 midi-values are *not* mapped to a 0..100 dB range; instead they are mapped to a -100..+28 dBfs range. this is what i meant by "28dB headroom" for amplifying low signals.
you cannot just map one range to another range.
mfg.asd.r IOhannes
PS: if someone can explain what i mean in a better english i would be greatful.