Support
Looper's Delight
|
Support |
|
|
|
hey gang-
I always wondered why these basic formulas
and charts weren't posted on the LD web site. Then I decided to do something
about it. I'm also cooking up a longer document that attempts to explain the
value of these formulas in practical applications. If any of you have any
comments, corrections, criticisms, etc. please post 'em where we can see 'em,
and I'll work 'em into the document in progress. My apologies if this fills up
too much of your mailbox.
dB, coyote
Delay Formulas We often find ourselves working with delay or sampling devices that do not easily or automatically sync to some other rhythmic source. You might have an audio delay device that displays delay time in milliseconds but does not sync to MIDI or some other time source. Or you might want to create a delay in sync with a source that has no time-sync signal. Or your so-called "sync-able" delay does not support the rhythms you wish to use. One quick solution is to use a "delay calculator" which can be found on several web sites. The best I’ve found is: http://www.jmaguire.com/audio_tools.php . In addition to numerous time-stretching and pitch-shifting calculators, it has a delay and frequency calculator that, given a tempo in beats per minute, will calculate delay times in milliseconds and pitch values in Hz for 11 different note values, from a dotted half note to a 32nd note. Another very good calculator – almost the same, in fact, and based on the same software, but without the 11-different-note-value calculator – is http://mp3.deepsound.net/eng/samples_calculs.php . A simple calculator can be found at http://www.guitar9.com/delaytime.html . I don’t use these web sites myself because I don’t keep a computer in my music studio (shocking but true), and I also like to figure things out for myself. It gives me a feel for the numbers and helps me to understand the "why" behind the calculations. If you’re of like mind, read on. The Magic Formulas delay time in milliseconds = [60 x 1000 / beats per minute] x [number of beats per cycle of rhythm/number of attacks per cycle] Some of you might already be familiar with this formula and the difficult "beats per cycle/attacks per cycle" fraction at the end. For you, I’m going to cut to the chase and simplify the formula, show its transformations, and give you the decimal equivalents of the 11 most common note values. You can copy this text and be done with it: DELAY FORMULAS
ms = [60000/bpm] x note value
bpm = [60000/ms] x note value
note value = [60000/bpm] /ms]
NOTE VALUES
whole note = 4
dotted half note = 3
half note = 2
dotted quarter note = 1.5
quarter note = 1
quarter note triplet = .666
dotted eighth note = .75
eighth note = .5
eighth note triplet = .333
sixteenth note = .25
sixteenth note triplet = .1666
Note/Hz/ms TRANSFORMATIONS Hz x 1.059463 = next higher note Hz x 2 = same pitch up one
octave Hz x 60 = bpm
ms/1.059463 = next higher note ms/2 = same pitch up one octave
60000/ms = bpm
ms = 1000/Hz Hz = ms/1000
* I know you’ll never use thousands of beats per minute, but you can use these numbers as a starting point, then divide by one of the note values above (4, 3, 2 ,1.5, etc. or a multiple thereof) to obtain some synchronicity between rhythm and pitch. |