d9 $ midicmd "start" # s "midi" d1 $ note ((scaleP scalePattern $ off 4 ((+ 2 ).slow 2) $ off 1 (inversion.slow 2) $ off 3 (inversion.slow 3) $ off 1.5 ((+ 2).rev.slow 2) $ generateMelodicSeed ))#s "[pe-gtr:10,midi]" #gain 1 #orbit 0 #midichan 1 d3 $ note ((scaleP scalePattern $ (rotR 4) $ (+ slow 8 "x" <~> ((0.25 ~>) generateMelodicSeed)) -- $ slow 4 \n $ generateMelodicSeed ))#s "[pe-gtr:8,midi]" #gain 1.2 #orbit 2 #midichan 3 hush

Digital Sampling

Sound (and analogous signals) are represented inside the computer in the form of samples. A sample is a snapshot of the signal’s amplitude value at a given point in time. These samples are collected at regular intervals. The speed at which the samples are collected is called the sample rate.

A signal is represented as a long stream of these sample values. (for example: [0 0.2 0.22 -0.1 -0.02 -0.5 -1 -0.66 ...] could be a signal inside the computer.)

The stream of sample values is converted to real sound (ie. pressure waves in the air) by a Digital Audio Converter (DAC) coupled with an amplifier and speaker. The DAC takes the sampled values and creates a smooth, continuous analog voltage by interpolating between the sample values using sinusoidal waves. This voltage is then typically amplified and fed to a speaker.

The sample rate affects what kinds of sounds can be accurately recorded and reproduced. Nyquist’s sampling theorem states that the highest frequency that can be accurately represented by a sampled recording is 1/2 the sampling rate. In modern computers, 44.1 kHz, 48 kHz, and 96 kHz are the most common sampling rates. If sample values fluctuate at more than 1/2 the sample rate, the tone will alias, resulting in in-harmonic distortion of the signal.


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