Sound

Sound

It may be commonplace to point out that acoustic reality and perceptual reality are different. In a live performance situation, for example, no matter how still the audience, the environment will be full of sounds extraneous to the music. If a tape recorder were positioned somewhere in the midst of such a situation, and if a segment of the resulting tape were submitted to digital sound analysis, the results would highlight the difference between what one heard during the performance (what is presumably captured on the tape), and what analysis confirms the tape actually contains. Sound analysis reveals the behavior of sound in the physical world. In this case, analysis would show that soundwaves from all the sound sources in the environment -- the various instruments of the performance, perhaps the stirring of the audience, or the sound of vehicles passing beyond the confines of the performance context -- the multitude of acoustic elements that make up each of these sounds do not remain conveniently grouped by source. Rather, the components of all these sounds mix together, combining into a single, very complex waveform which is represented on the tape and revealed through analysis. This is because sound waves are additive, like waves in water, multiplying in quality rather than quantity.

In the simplest possible terms, what digital analysis uncovers are the acoustic features of the sounds captured by the tape recorder; what are actually heard are the perceptual features of the same sounds. The acoustic and perceptual characteristics of sound are not the same, nor in many cases is there a one-to-one correspondence between them.

Parameters of Sound

In a very general sense, sounds in a normal environment consist o...

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...on provided by either form of presentation is an approximation at best, limited by the resolution capabilities of both the digitizer and the analyzer, as well as by the fineness of detail possible in the graphic display of the software. It is also important to be cautious in considering which details of the visual representation of a sound sample are salient to the sound as perceived; often the picture of a sound will include clearly visible elements which are acoustically present in the sound but too short in duration, or too soft in intensity to register perceptually. A useful maxim in this regard is the following: If a discrete element is filtered from a sound with no difference to the resulting tonal sensation, then the element is unimportant to the final percept and need not be considered in interpreting the data, no matter how blatantly it appears in analysis.