Sound In Software

We can represent any audio signal as a set of discrete values if we make each value a sample of the amplitude of the signal at a point in time and the time between samples a constant interval. This process is shown in the following figures. Figure 1 shows an input signal, in this case a sine wave.

1 - Continuous signal

We can sample the amplitude of the signal at a regular interval to obtain the values shown in Figure 2 and store those values in a computer file.

2 - Sampled waveform

The recorded samples can later be sent through a digital to analog converter (DAC) to produce a varying voltage that will drive an audio amplifier and loudspeaker. The output is a series of steps as shown in Figure 3. When the stepped output is passed through a smoothing filter, the final output is a continuous signal identical to the input signal.

3 - Sample Output

The representation of a signal by a set of samples is the foundation of all digital audio systems, including both CD audio and digital sound synthesizers. Since the sound is represented by a set of numbers, a computer can calculate the sample values directly rather than by sampling an analog input signal. Simply put, a digital sound synthesizer produces sound by generating a series of samples representing the instantaneous amplitude of the signal at a constant time interval. Samples can be directly calculated, from a recorded sound, or any mixture of the two. In addition, samples can be processed with filters and other sound effects by direct calculations on the samples. Thus, a digital synthesis system can produce a wide variety of sounds, both natural and synthetic, limited only by capacity of the computer system and the imagination of the musician.