Digital Recording

A recent development where, in contrast to the conventional analog tape recorder, the audio signal is sampled within a set of pre-defined limits. It is thus the reciprocal process to that described as digital sound synthesis. Digital sampling is also used is some digital sound synthesizers. See: Tape Recording.

In a typical digital recorder the input signal is first filtered to remove any frequencies that cannot be accurately represented digitally. Then the instantaneous amplitude of the signal waveform is sampled at a rate at least twice as high as the highest frequency which remains after filtering (at least 40,000 times per second in the case of 20 kHz, for example). The sampling process results in a steady stream of instantaneous signal-waveform values (1/40,000 of a second or 25 microseconds apart for the instance quoted). The standard sampling rates for digital recording are 44.1 and 48 kHz. See: Transient Response.

An analog-to-digital converter (ADC) which performs this sampling process expresses these values as binary numbers, and it is this digital information, rather than the analog waveform itself, which is recorded on magnetic tape, computer memory or other storage medium. The playback process recovers the numbers from the storage medium (see diagrams under magnetic tape and sound synthesis). Compare: Transducer.

When a digital signal is copied, there is no increase in noise or added distortion, provided no errors have occurred. The opposite is true in analog to analog dubbing of magnetic tape. A second major advantage of digital recording is that a dynamic range in excess of 90 dB can be achieved with 16-bit samples, whereas with analog techniques, the available range, and therefore the maximum signal-to-noise ratio, rarely exceeds 60 dB. Finally, since individual samples may potentially be accessed, editing is considerably more accurate than that achieved with the usual tape splice, although it must be performed with the use of software, not manually.

See: VU Meter. Compare: Binaural Recording, Electronic Music, Musique Concrete, Tape Music.