Specifications

converter 1.5

2000 - 2005 urr Sound Technologies Inc.
45
audio input
Audio to midi conversion in converter is performed on the basis of amplitude, in one of two modes: a
continuous time-varying conversion mode for continuous controller applications, and a trigger/gate
conversion mode useful for using an audio source to trigger midi note on / note off messages.
Note
that only the line-input is used on all the soundcards – the mic input is not supported.
On the
SoundBlaster 16, SoundBlaster Pro and compatibles (as well as the Gravis Ultrasound), converter
automatically sets the level for the line input to its maximum position so that an external mixer program
is not needed.
Each audio channel generates a stream of single value bytes, based on the amplitude of the incoming
audio, which can be inserted into any data byte in a particular midi message type. The associated midi
message data which encapsulates the converted value bytes is defined in the audio parameters menus.
As an example, the following steps would program the audio conversion engine to generate a
continuous stream of modulation wheel data (continuous controller) from the left (non-filter) input
channel. This is assuming that the main audio input is enabled and converter is operating in audio input
mode.
Step 1: program the midi conversion settings
•
go to the audio parameters menu section (F3), press [F7] for the midi conversion settings menu,
then [F5] for midi data settings, and finally [F6] for the main audio channels parameters.
•
type 2 for the left conversion byte position parameter, 176 for the left statusbyte (or use the page
up / page down keys to scroll until the parameter reads “cntrl [ch. 1]”), then type 1 for the left 1
st
databyte value (or scroll until the parameter reads “mod wheel”), and leave the left 2
nd
databyte
value at zero. This tells converter that the converted value byte should be used for the 2
nd
data byte
in the midi message, and that the type of midi message to generate is a controller message on midi
channel 1 (by using 176 as the status byte). By setting the 1
st
data byte in the message to a 1, we
have specified the controller message type to be modulation wheel.
•
move the cursor to the left convert mode parameter and choose continuous controller mode (“cont.
ctrl”), then select “no conversion” for the right convert mode parameter.
Step 2: specify the midi data reduction settings (optional)
Since continuous-controller type of audio conversion can generate a tremendous number of midi
messages per second, especially if more than one audio channel is being used, it can be useful to
program the data thinning algorithms to intelligently reduce the density (messages per second) of the
generated midi stream.
•
press [F8] twice to back up in the menu hierarchy, then press [F6] for data reduction settings.
•
there are two parameters for each of the six audio channels; the parameters for the main audio
channels (non-filter channels) are the first four on the left of the menu screen. Try a value of 5 for
the left continuous controller reject parameter (labeled “left cc reject” on the menu), and a value of 6
for the left channel reject threshold parameter (labeled “left reject thresh.”). These settings mean
that out of every 5 audio byte conversions, only 1 is transmitted, unless there is a sudden change in
the audio amplitude that exceeds the threshold (which we set to 6). If the latter happens, a midi
message is transmitted instantly (data rejection does not occur) in order to preserve the musically
important transients of the audio, while reducing the amount of unnecessary midi data.
That’s all there is to it. If for some reason no data is being generated (and yet you can see audio input in
the oscilloscope or system / audio info display panels), check to make sure the input gates are not
interfering by setting the left threshold parameter to 0 in the main audio gates settings menu.
Additionally, you may want to experiment with the arithmetic processing that can be applied to the
channel allowing such processing as amplitude compression or expansion (using a combination of
division and addition or multiplication and subtraction operands respectively).