Alen Koebel
2010-01-27 18:21:03 UTC
Re-posting - forgot the subject line!
-----------------------------------
My first post here. Be gentle. ;-)
I'm trying to find out how the D-50 (and D-550, D-10,
D-110, D-20 & MT32) simulates a resonant filter. I say
"simulates" not "models" because I doubt there is an
actual discretized model of a filter in the synth
engine. The evidence for this is (a) the fact that
samples (short though they were) cannot be processed
by the "filter" - it "processes" only pulse and saw-
tooth waveforms, (b) a block diagram in the D-50 manual
seen here http://homepage.mac.com/synth_seal/html/d110.html
shows pulse-width controlled waveforms being created,
then processed ("filtered") in some way to add resonance,
then multiplied (ring modulated) by a synchronous sine
wave to get a sawtooth-like waveform. The "filter" block
is where the magic happens. "Magic" is a relative term -
the filter sounds real enough to my ears (I have a D-10)
but doesn't have the silky-smooth quality we associate
with a well-modeled filter.
I've searched the music-dsp archives, as well as the
synth-diy archives and the electro-music.com forums,
but came up dry. General Iternet searches came up with
only one idea but I admit I don't fully understand the
description:
http://www.kvraudio.com/forum/viewtopic.php?p=3747093
Any pointers or ideas? Maybe the above idea is spot on
and I'm just not understanding it, so any help in that
direction would be appreciated too.
-----------------------------------
My first post here. Be gentle. ;-)
I'm trying to find out how the D-50 (and D-550, D-10,
D-110, D-20 & MT32) simulates a resonant filter. I say
"simulates" not "models" because I doubt there is an
actual discretized model of a filter in the synth
engine. The evidence for this is (a) the fact that
samples (short though they were) cannot be processed
by the "filter" - it "processes" only pulse and saw-
tooth waveforms, (b) a block diagram in the D-50 manual
seen here http://homepage.mac.com/synth_seal/html/d110.html
shows pulse-width controlled waveforms being created,
then processed ("filtered") in some way to add resonance,
then multiplied (ring modulated) by a synchronous sine
wave to get a sawtooth-like waveform. The "filter" block
is where the magic happens. "Magic" is a relative term -
the filter sounds real enough to my ears (I have a D-10)
but doesn't have the silky-smooth quality we associate
with a well-modeled filter.
I've searched the music-dsp archives, as well as the
synth-diy archives and the electro-music.com forums,
but came up dry. General Iternet searches came up with
only one idea but I admit I don't fully understand the
description:
http://www.kvraudio.com/forum/viewtopic.php?p=3747093
Any pointers or ideas? Maybe the above idea is spot on
and I'm just not understanding it, so any help in that
direction would be appreciated too.