Technical Stuff; Microtuning And Music Perception; Why The Moog Filter (Filter 2) Attenuates Bass - Alesis Andromeda A6 Tips And Tricks Manual

21.1 microtuning and music perception

Michael Caloroso wrote:
I've heard that the ear perceives sounds tuned sharp as bright and sounds tuned flat as darker.
Orchestras have been slowly increasing their center of pitch for this reason (I've heard).
Because they are not on a fixed scale, string sections will do this to enhance the effect of the music.
Altering the minor or major third a few tenths of a cents during a sad motif is more effective to stir
those emotions. Anybody who has seen the final "ascending" scene in "Ghost" with the strings
playing "Unchained Melody" and felt that tear in their eye has witnessed this effect.
Many of the traditional instruments aren't even scaled the same, they're not all equal. If you have a
trumpet player and a clarinet player play the same scale their notes won't all be in tune. Not even
the guitar is scaled right either. It's these "errors" in scaling that gives the orchestra its life.

21.2 microtuning and music perception

Mike Peake and Jeff wrote:
Are the three LFO noise outputs independant of each other and the audio noise output? In other
words, if I modulate the two filters with two different LFO noises, will they actually be modulated in
the same way?
--PBr
The analog noise is entirely separate from the LFO Noise waveforms. I'm listening to an edit in
which I've got both filters modulated by different LFOs which are set to NOISE and whose Triggers
are OFF and Freerun is ON. They -appear- to be independent, but the LFO NOISE is technically
limited compared to the analog Noise to begin with.. I can't answer the question. Jeff? Are you still
lurking about?
Yes... lurking... shhhhhhhhhh....... ;)
There is one global random number generated every cycle (2ms). The LFOs are run on a different
timebase from the random number generator. Each LFO grabs the current global random number
and uses that as it's noise output. So while it's possible that more than one LFO will use the same
number, in practice the random number changes often enough that each LFO will have a unique
output.

21.3 why the moog filter (filter 2) attenuates bass:

(warning -- technical!)
Michael Caloroso wrote:
The Moog transistor ladder filter is a set of five pairs of transistors with a single transistor at the
bottom to control the standing current, or the cutoff frequency, of the ladder. Four of the middle
transistor pairs each have a capacitor between the collectors; by varying the standing current in the
ladder you vary the emitter resistance, and combined with the cap at the collector this forms a one
pole filter. Four of these stacked on top of one another forms the four pole filter we all know and
love. The fifth pair of transistors at the top of the ladder is the balanced current source for the entire
ladder.
section 21: technical stuff
really technical stuff