DSP

What is DSP?

DSP (Digital Signal Processing) can be described as the manipulation or transformation of a Discrete signal by means of arithmetic and mathematical formulae. But there are 2 classifications for audio signals to be considered:

1.  Discrete
2. Continuous

Continuous signals can be described by analysing the analogue synthesizer and its oscillator outputs. The circuitry involved to generate such signals consists of 2 elements of control, signal amplitude (volume) and signal frequency (pitch). These have been implemented with additional analogue circuitry to enable voltage control of the elements. i.e. Voltage Controlled Oscillators (VCO’s) and Voltage Controlled Amplifiers (VCA’s), where the voltage applied at the input of the VCA is directly proportional to the level of signal amplification and the voltage applied to the input of the VCO is directly proportional to the frequency that it generates.

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By considering the function of the VCO in greater detail, it is possible to understand the distinction between Continuous signals and Discrete signals. Once the VCO is ‘triggered’ by a real voltage at the input the circuitry begins to oscillate, and the output signal performs a cycle. The cycle characterises signal ‘tone’ or ‘timbre’, but the frequency by which the cycle repeats every second will determine the pitch of it. The cycle type has been available on most early analogue synthesizers as the following wave types:

•  Square
• Triangle
• Saw
•  Pulse

… and the most basic of all is the

•  Sine wave, derived from the trigonometric function for a sinusoid.

For analogue oscillators, there are infinite possibilities to determine a particular cycle/period regardless of the duration of it in terms of time. This characterises the signal as a Continuous signal.

A Discrete signal on the other hand does not have infinite possibilities. It is governed by two factors, Sampling rate and Sampling resolution. Sampling rate is defined as the number of samples collected at regular intervals to represent a signal over one second. Figure 1.1a shows a Continuous sine wave generated by an analogue synthesizer, and Figure 1.1b shows a close up of a single period of the same sine wave, that has been sampled, i.e. converted into a Discrete – time – signal.