LIL and sndkit: an overview

LIL and sndkit: an overview

What is LIL?

LIL (Little Interpreted Language) is a tiny scripting language included with sndkit. Using LIL, one can connect various sndkit algorithms together to build up sounds and patches.

Syntactically, LIL looks very similar to TCL:

print hello world

Will print "hello world". The general format is to have words separated by spaces. The first word is the command, the following words are the arguments.

Sndkit functions

sndkit adds several functions to LIL. Most of these are sndkit algorithms wrapped into a unit generator that takes in input signals and returns one or more output signals.

The following code can be used to produce a sine wave at 440Hz with an amplitude of 0.5:

sine 440 0.5

If you were to run this program, you wouldn't hear any sound. To get sound, the output of the sine wave would need to be written to a WAV file. And then some audio would need to be computed.

The following code creates a 10 second WAV file of a sine:

wavout [sine 440 0.5] "sine.wav"
computes 10

Using the brackets [], the sine wave signal is computed and sent as input to the WAV file writer wavout, writing to a file called "sine.wav". The computes command runs the patch for 10 seconds.

One could use nested brackets to build s-exprsdsion like constructs. This creates a sine wave whose pitch is being modulated by another sine wave to create vibrato:

sine [add [param 440] [sine 6 50]] 0.5

Add adds two signals together, in this case a constant 440 and a sine wave at 6Hz with an amplitude of 50. This causes the sounding sine wave oscillator to go up 50Hz and then down 50hz.

The param function starts needing to be used when arguments mix and match constants and evalulated signals using brackets. Any constants that appear before bracketted arguments need to use param. This is why the 440 constant needs a param, and the 0.5 does not require one (though it doesn't hurt to add). It's a weird quirk that has to do with evaluation order and how things work under the hood, but one gets used to it.

To print a list of all the available functions in LIL, use the lscmds function:

echo lscmds | sndkit

The 'zz' operator

Brackets and s-expressions can be fun, but they can get very unwieldy very quickly in LIL, especially since backslashes are required to break up commands across different lines.

The previous vibrato example can be rewritten without brackets using a special function called 'zz':

sine 6 50
add zz 440
sine zz 0.5

zz itself doesn't do anything. It is a placeholder that tells the function to use the argument that has been implicitely generated.

This can be quite funny looking and confusing at first. This concept can be best grokked by understanding the stack-based operations that are actually happening to build this patch.

Using postfix notation as seen in Forths and Forth-like languages, the patch above can be realized in the following way:

440 6 sine 440 add 0.5 sine

This can be read left-to-right:

440 and 6 are pushed to the stack.

sine pops 6 and 440, computes a sample, and pushes it on the stack.

440 is pushed to the stack.

add pops 440 and the sine sample, adds them together, and pushes the result onto the stack.

0.5 is pushed onto the stack.

A sine function pops the 2 items off the stack and computes the sine that gets heard.

Going back to LIL, zz tells a function to pop the last item off the sndkit stack and use that as an argument. Note that zz only works with sndkit nodes and things working with the sndkit stack. It is not a part of LIL!

Stack Operations

It was mentioned in the previous section that under the hood sndkit works using a stack. A few stack operations have been exposed to LIL.

The most common stack operation used dup, which duplicates the last item on the stack. If the item is a signal (it typically is), it will efficiently make a copy of this signal so it can be used as an input for another unit generator.

The following code below is a patch of subtractive sawtooth oscillator being fed into a delay line. The dup operation here makes a copy of the saw (blsaw) and feeds it into the delay line with feedback (vardelay).

# create a trigger signal
metro 0.5

# feed signal into envelope generator
env zz 0.001 0.01 0.1

# create saw oscillator at middle C
blsaw [mtof 60]
butlp zz 800

# multiply envelope and saw
mul zz zz

# reduce gain a bit to prevent clipping

mul zz 0.7

# make a copy of the dry signal

# process dry signal with delay line and filter it
vardelay zz 0.5 0.75 1.0
butlp zz 300

# add dry and wet signal together
add zz zz

# write output to WAV file
wavout zz "test.wav"

# compute 10 seconds of audio
computes 10

The drop operation will drop the last item of the stack. Here it is being used below to discard one of the channels of the stereo reverb processor bigverb. dupis also being called twice here. Once to make a copy of the dry signal, and then again for the stereo inputs for the reverb.

# create an LFO at 0.2hz
sine 0.2 1

# scale the LFO to be between 250-400hz
biscale zz 250 400

# feed scaled LFO into frequency of sawtooth oscillator
blsaw zz

# filter the sound and scale it
butlp zz 800
mul zz 0.3

# make a copy of the dry signal
# copy the signal for mono->stereo inputs

# process stereo signal using bigverb
bigverb zz zz 0.93 10000

# drop one of the outputs (right channel)

# scale the remaining channel
mul zz 0.1

# add wet and dry signals
add zz zz

# write to WAV file and compute
wavout zz "test.wav"
computes 10

Registers and Buffer Holding

For signals that get used more than once throughout a patch, it is best to use buffer holding and registers.

Various unit generators talk to eachother by reading and writing to small chunks of signals known as buffers. Under the hood, there is a fixed number of buffers to write to, which are managed automatically using something called a buffer pool. When a signal is done using a buffer (the signal is no longer being used), that buffer is released. This can be process can be prevented by manually marking the buffer. This is known as holdingthe buffer. A held buffer must be explicitely unheld when it is done. Otherwise, the buffer will never be used again (which can cause trouble later).

To store and retrieve buffers, sndkit provides a register system. There are a total of 16 registers available.

The following example below creates a sirenpatch. Here, an LFO signal is being used to control filter cutoff and frequency of a sawtooth oscillator. When the LFO signal is created, is is held and stored in register 0 via regset and hold. The signal can then be retrieved again using regget. When it is finished, the buffer is released using unhold.

# create an LFO. hold and store in register 0
sine 0.2 1
hold zz
regset zz 0

# scale the LFO and to modulate sawtooth
biscale [regget 0] 215 430
blsaw zz
mul zz 0.5

# scale the LFO to modulate filter cutoff
biscale [regget 0] 100 1000
butlp zz zz

# unhold the LFO signal
regget 0
unhold zz
regclr 0

# write to wave
wavout zz "test.wav"
computes 10