by Paul Batchelor
# Bones # By Paul Batchelor # September 2016
Bones is a quick sporthlet I made to get back into the habbit of making sporthlets. It primarily utilizes modal synthesize and variable feedback delay lines to achieve something vaguely bone like (well, at one point it was).
Tables and variables
The first table created is a set of modal ratios approximating a uniform wooden bar ratios. They have been obtained from http://www.csounds.com/manual/html/MiscModalFreq.html.
_rat "1 2.5752 4.4644 6.984" gen_vals
Variables are a relatively new concept in Sporth, and have their own commands for setting and getting. tk is a variable that will hold the trigger tick, and frq will eventually hold the fundamental frequency of the instrument.
_tk var _frq var
The base trigger is a metronome, whose rate is randomized via a randh module.
1 10 1 randh metro
A consistent metronome can annoying quickly, so it is sent through a maytrig to hush it up every now and then. The probability randomly swings between 0.1 and 0.8 via randi. To make the line a little less regular, the rate gets changed with randh.
(0.1 0.8 (1 10 3 randh) randi) maytrig
The maytrig reduces the density, but phrasing is also important. for this reason, the output of the maytrig is multiplied by a maygate. (Could this have been done with just one maytrig? Probably. But that I did not think of this in the moment of creating this)
dup 0.65 maygate *
tick is added onto the trigger signal, to ensure that there is a trigger at the start of the sporth drawing.
The entire signal is assigned to the variable tk via the set ugen.
An entire explanation of modal resonators and modal synthesis are beyond the scope of this sporthlet, but a small one will be given. One can think of a modal filter as a filter that resonants at a particular Q and frequency. In modal synthesis, an excitation signal (in this case, a trigger signal), is fed through a bank of modal filters, configured in both series and in parallel. What comes out is the sound. This technique is largely used in physical modelling.
The base frequency of the instrument is set via trand, who trigger is obtained from the previously set variable tk.
_tk get 500 1500 trand _frq set
The trigger signal tk is sent through two modal filters in series, whose frequences are obtained from the first two elements table rat, multiplied by the frequency frq. In the first modal filter, the Q is being randomized via randi.
_tk get (_frq get 0 _rat tget *) 10 40 3 randi mode (_frq get 1 _rat tget *) 20 mode
The process is repeated again, this time with the last two modal frequency ratios in rat, and different Q values (by the way, these Q values were chosen fairly randomly with a little experimentation)
_tk get (_frq get 2 _rat tget *) 22 mode (_frq get 3 _rat tget *) 15 mode +
The variable delay line is the crucial element that adds a strange crittery characteristic to the sound. This is done by randomizing the feedback and delay times with randi.
dup 0.1 0.8 3 randi 0.001 0.2 (0.1 4 1 randi) randi 1.0 vdelay
To add more texture to the delay line, a smoothdelay is applied to the variable delay signal. A smooth delay line is like a variable delay line, except there is no residual pitch modulation. Randi is used to control feedback, and sine is used to control delay time. To add space and variation, the level is modulated by yet another randi.
dup 0.4 0.9 0.5 randi 0.2 1 sine 0.01 0.3 biscale 1.0 64 smoothdelay 0 1 0.2 randi *
Finally, the delay lines and dry signal are summed together.
The final effects used are a gentle chowning reverb fed through a hard limiter limit.
dup jcrev -6 ampdb * + -1 1 limit