gensound 0.2

Pythonic audio processing and synthesis library

Gensound

The Python way to audio processing & synthesis.

An intuitive, flexible and lightweight library for:

• Experimenting with audio and signal processing
• Creating and manipulating sounds
• Electronic composition

Core features:

• Platform independent
• Very intuitive syntax
• Easy to create new effects or experiments and combine them with existing features
• Great for learning about audio and signals
• Multi-channel audio for customizable placement of sound sources
• Parametrization
• And more to come!

Setup

1. Install using pip install gensound. This will install NumPy and SimpleAudio, if needed.

2. Run the examples below (or some of the example files in the repository).

Show Me the Code

• Load a WAV into a Signal object from filename:

from gensound import WAV, kushaura

wav = WAV(kushaura) # load sample WAV

• Playback or file export:

wav.play()
wav.export("test.wav") # only WAV supported

• Play file using different sample rate:

WAV(kushaura).play(sample_rate=44100) # original sample rate 44.1 kHz

• Mix a Stereo signal to mono:

wav = 0.5*wav[0] + 0.5*wav[1] # sums up L and R channels together, halving the amplitudes

• Switch L/R channels in stereo WAV file:

wav[0], wav[1] = wav[1], wav[0]

• Attenuate R channel by 3dB:

wav[1] *= Gain(-3)

• Crop 5 seconds from the beginning:

wav = wav[:,5e3:] # both channels, 5000 ms onwards

or even easier:

wav = wav[5e3:] # channels omitted; 5e3 is float, automatically interpreted as ms

• Grab the first 1000 samples:

wav = wav[:,:1000] # samples are in ints, so don't omit channel slice

• Repeat a signal 5 times:

wav = wav**5

• Add a 440Hz sine wave to the L channel, 4 seconds after the beginning:

from gensound import Sine

wav[0,4e3:] += Sine(frequency=440, duration=2e3)*Gain(-9)
wav[0,4e3:] += Sine(frequency="A4", duration=2e3)*Gain(-9) # or like this

• Reverse the R channel only:

from gensound import Reverse

wav[1] *= Reverse() # use Reverse transform, or:
wav = wav[1,::-1] # manually reverse the samples

• Haas effect - delaying the L channel by several samples makes the sound appear to be coming from the right:

wav[0] *= Shift(80) # lisen with headphones! try changing the number of samples

• Stretch effect - slowing down or speeding up the signal by stretching or shrinking it. This affects pitch as well:

wav *= Stretch(rate=1.5) # plays the Signal 1.5 times as fast
wav *= Stretch(duration=30e3) # alternative syntax: stretche or shrink the Signal into 30 seconds

• Imitate electric guitar amplifier and reverb effect:

from gensound.amplifiers import GuitarAmp_Test
from gensound.effects import OneImpulseReverb

guitar = WAV("guitar_clean.wav")

guitar *= Gain(20)*GuitarAmp_Test(harshness=10, cutoff=4000)*OneImpulseReverb(mix=1.2, num=2000, curve="steep")

• AutoPan both L/R channels with different frequency and depth

from gensound.curve import SineCurve

s = WAV(kushaura)[10e3:30e3] # pick 20 seconds of audio

CurveL = SineCurve(frequency=0.2, depth=50, baseline=-50, duration=20e3)
# L channel will move in a Sine pattern between -100 (Hard L) and 0 (C)

CurveR = SineCurve(frequency=0.12, depth=100, baseline=0, duration=20e3)
# R channel will move in a Sine pattern (different frequency) between -100 and 100

t = s[0]*Pan(CurveL) + s[1]*Pan(CurveR)

Syntax Summary

Meet the two core classes:

• Signal - a stream of multi-channeled samples, either raw (e.g. loaded from WAV file) or mathematically computable (e.g. a Sawtooth wave). Behaves very much like a numpy.ndarray.
• Transform - a process that can be applied to a Signal (for example, reverb, filtering, gain, reverse, slicing)

By combining Signals in various ways and applying Transforms to them, we can generate anything.

Signals are envisioned as mathematical objects, and the library relies greatly on overloading of arithmetic operations on them, in conjunction with Transforms. All of the following expressions return a new Signal object:

• amplitude*Signal: change Signal's amplitude by a given factor (float)
• -Signal: inverts the signal
• Signal + Signal: mix two signals together
• Signal | Signal: concatenate two signals one after the other
• Signal**4: repeat the signal 4 times
• Signal*Transform: apply Transform to Signal
• Signal[start_channel:end_channel,start_ms:end_ms]: Signal sliced to a certain range of channels and time (in ms). The first slice expects integers; the second expects floats.
• Signal[start_channel:end_channel,start_sample:end_sample]: When the second slice finds integers instead of floats, it is interpreted as a range over samples instead of milliseconds. Note that the duration of this signal changes according to the sample rate.
• Signal[start_channel:end_channel]: when a single slice of ints is given, it is taken to mean the channels.
• Signal[start_ms:end_ms]: if the slice is made up of floats, it is interpreted as timestamps, i.e.: Signal[:,start_ms:end_ms].

The slice notations may also be used for assignments:

wav[4e3:4.5e3] = Sine(frequency=1e3, duration=0.5e3) # censor beep on seconds 4-4.5
wav[0,6e3:] *= Reverb(...) # add effect to L channel starting from second 6

Slice notation may also be used to increase the number of channels implicitly:

wav = WAV("mono_audio.wav") # mono Signal object
wav[1] = -wav[0] # now a stereo Signal with R being a phase inverted version of L

Note the convention that floats represent time as milliseconds, while integers represent number of samples.

The overloading of basic arithmetic operators means that we can generate complex signals in a Pythonic way:

f = 220 # fundamental frequency
sawtooth = (2/np.pi)*sum([((-1)**k/k)*Sine(frequency=k*f, duration=10e3) for k in range(1,11)])
# approximates a sawtooth wave by the first 10 harmonics

When performing playback or file export of a Signal, Gensound resolves the Signal tree recursively, combining the various Signals and applying the transforms.

More

See the Reference for a growing list of useful signals and transforms. We also plan to upload more example code. To get a better understanding of the underlying code, the reader is invited to the Technical Guide. If you are interested in contributing, check out Contribution.

Topics not yet covered

• How to extend Signal and Transform to implement new effects
• Crossfades and BiTransforms
• Curves and parametrization
• Custom Panning Schemes