The Interpretation of MIDI Velocity.
Roger B. Dannenberg · 2006
The MIDI standard does not specify how MIDI key velocity is to be interpreted. Of course, individual synthetic instruments respond differently, but one would expect that on average, instruments will respond about the same. This study aims to determine empirically how hardware and software MIDI synthesizers translate velocity to peak RMS amplitude. Analysis shows synthesizers roughly follow an x-squared rather than exponential mapping. Given a desired dynamic range (from velocity 1 to 127), a square-law mapping from velocity to RMS is uniquely determined, making dynamic range a convenient way to summarize behavior. Surprisingly, computed values of dynamic range for commercial synthesizers vary by more than 60dB.