Music 171 homework 5
Practice with abstractions: this assignment is to build an additive
synthesis instrument that can imitate the Hammond organ sound. The Hammond
organ had a set of eight "drawbars" (sliding potentiometers) that set the
amplitudes of the first
eight partials (harmonics) of the output tone. (There were lots of other
features as well, but this is the one of interest here.) Your patch need not
be polyphonic (it should be designed only to play one note at a time) but
you should use the abstraction mechanism to make the eight overtones (each
copy of the abstraction should make one of them).
Two novel features are, first, being able to use a "$" sign inside an
object box to differentiate between the harmonics; and using the "moses" object
to allow pitches below 10 (for example) to simply turn the
sound off, so that you can make sequences with rests in them.
Your successful patch should sound like
To make the patch:
- Make a main patch with two tables, "sequence" (as before, but now try using
16 points instead of 8 with range set from 128 to 0 so you can store MIDI
pitches in it conveniently. My numbers are 35 42 49 0 37 0 64 0 0 44 47 34 46
67 72 58.) and "drawbars", 8 values, ranging from 1 to 0. (Remember the range is
set from the top of the graph to the bottom, which is why the range is specified
backwards here). Make the usual counter arrangement to read through he values
of "sequence". To make it easy, you can just use a "send" object to send the
pitches into the abstraction. (In a later step, you will want to insert a
"moses" object before the send to split off pitches that should be interpreted
as "turn off" instead of a real pitch.)
- Make an abstraction named, for instance, "partial", and invoke eight of
them, as "partial 1", ..., "partial 8". Then you can use "$1" inside the
abstraction to do things that depend on the partial number. To start with,
get the pitch (preferably in the simplest possible way, using a "receive"
object), convert to frequency, multiply by "$", and use this as the frequency
of an "osc~". This will make a sinusoidal tone at the harmonic.
- Arrange to add up all the sounds (using outlet~, or by adding them
cumulatively as in the D07.additive.pd example) and multiply the result
by a line~ to turn it on and off. Just an attack and release shape will be
adequate for this example, and they may be fixed messages "1 10" and "0 10".
- Insert a "moses 20" object between the sequencer and the "send"
that gets the pitches into the abstraction. When the pitch is >= 20 (right
outlet of moses), send the pitch and turn on the line~. When the pitch is < 20,
just turn off the line~. You now should have a sequencer that makes "rests"
whenever the pitch is 0 or close to 0.
- Inside the abstraction, arrange to read the amplitude from the "drawbars"
table. The easiest way to do this is to use "loadbang" into "f $1" which
will generate a message whose value is the number of the partial, starting at
one; then subtract 1 to make an input to a tabread~ object. This can be
multiplied directly by the output of the osc~ to control its amplitude.
Make an on/off control (to start/stop the sequencer and the usual output
level control, and make a zip archive of the main patch and the abstraction
together (preferably in a directory with your name in the directory name to
make it easy to find once unzipped).
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