08-table-lookup.py - Table as transfer function.

In computer science, a lookup table is an array that replaces runtime computation with a simpler array indexing operation. The savings in terms of processing time can be significant, since retrieving a value from memory is often faster than undergoing an “expensive” computation.

This technic is also used a lot in audio synthesis, where the waveform can be pre-computed and stored in a table, then simply readed with a ramp at the desired frequency.

from pyo import *

s = Server().boot()

src = SfPlayer("../snds/flute.aif", loop=True)

# Arctangent transfer function table.
table = AtanTable(slope=0.5, size=512)

# A signal to dynamically control the drive of the transfer function.
drive = Sig(0.5)

# We give it True to the dataonly argument when opening the sliders window,
# otherwise the table would be rewrite way too often.
drive.ctrl([SLMap(0, 1, "lin", "value", 0.5, dataOnly=True)], title="Transfer fonction slope")

# Lookup reads a table given an audio index lying between -1 and 1.
# It is especially designed to scan a transfer function with an audio signal.
look = Lookup(table, index=src, mul=0.5).out()

# Function called to redraw the transfer function.
def redraw():
    table.slope = drive.get()

# We call the "redraw" function every time the "drive" value changes.
trig = TrigFunc(Change(drive), function=redraw)

sc = Scope(look)