Transition from analog to digital sound reference

No system can be perfect. In order to capture a live performance through a microphone or a direct electric input from, say, a synthesizer, the input signal must be processed by electronics which inevitably introduce distortion into the original signal. Indeed, the microphone and eventually the loudspeaker often add more unwanted components to the signal than the amplifier does. The original signal can be recorded on tape as a series of varying magnetized stripes in an oxide coating or, on disc, as a wavy groove in the surface plastic.

Most recently, the best recordings have been produced as a series of digital pulses encoded on a special light reflecting disc, scanned by the laser of a compact disc player to recapture the original signal. Digitally encoded music, recorded direct, offers the purest signal. The electronics that decode the series of pulses, which are turned eventually into sound waves, allow none of the spurious distortion signals that are associated with other ANALOG types of recording.

Modern hi-fi systems accept a variety of input sources — tape, disc, AM RADIO, FM RADIO or digital disc. It is in the reproduction of the recorded signal that the psychoacoustician makes a significant contribution — although if material is originally recorded with multidirectional microphones to produce a set of signals that can be subsequently processed electronically the task of the hi-fi system can be made simpler.

The simplest such technique is stereophony. Original music is recorded with two microphones set at an angle to each other, so they pick up slightly different signals. If the music is electronic in origin, pseudo-stereo parallel tracks can be produced. The two signals are recorded and amplified separately and fed to two loudspeakers spaced some distance apart in the listening room. Because the PHASE of the sound waves coming from each speaker is different – the waves from one speaker are slightly out of step with those from the other – the ear is fooled into hearing a complete sound image spread between the two speakers, with different instruments and singers apparently coming from different directions; much like a 3-D image.

Further developments of this type of aural trickery have involved four or more loudspeakers and specially encoded program sources. Overall, the technique is known as ambisonics and its intention, like that of the original stereo systems, is to recreate the exact sound field perceived by a listener in a natural acoustic. Its exact working depends on the ability of the electronics to manipulate the phase and loudness of the sound fed to each speaker. The most sophisticated ambisonic systems can literally change the perceived acoustics of the same piece of music from a country village hall to a grand concert hall at the flick of a switch.