First you hear a 440Hz sinsuoidal tone distorted by a symmetrical compressor. It alternates with its third harmonic.
Next the 440z tone is distorted asymetrically by a half wave rectifier. The distorted toine alternates with its second harmonic
Now two tones of 700 and 1000 Hz distorted by a symmetrical compressor. These tones alternate with a 400Hz pointer to the cubic difference tone.
You will hear a 440 Hz pure tone plus its second harmonic added with the phase varied from -90 to +90 degrees. This is followed by the same tones distorted through a square law device.
This demonstration illustrates some audible effects of distortion external to the auditory system. These effects are of interest, not only because distortion commonly occurs in sound recording and reproducing systems, but because distortion is an important topic in auditory theory. This demonstration replicates one presented W.M.Hartmann in the "Harvard tapes" (Auditory Demonstration Tapes, Harvard U: versity, 1978). Both harmonic and intermodulation distortion are illustrated.
Our first example presents a 440-Hz sinewave tone, distorted by a symmetrical compressor.
A symmetrical compressor has an input-output relation such as that shown at the left. The important property is that the function describing the relation between input and output is an odd function-that is, f(x) is equal to -f(-x). Because of the symmetry, only
odd harmonics of the original sinewave are present in the output. A simple example of a symmetrical compressor would be a limiter. In this demonstration, the distorted to alternates with its 3rd harmonic (which serves as a "pointer").
Next the 440-Hz tone is distorted asymmetrically by a half-wave rectifier, which generates strong even-numbered harmonics. The distorted tone alternates with its 2nd harmonic. When two pure tones (sinusoids) are present simultaneously, distortion produces not only harmonics of each tone but also tones with frequencies nIl - m/2, where m and n are integers. The prominent cubic difference tone (2/1 - 12) which occurs when tones of 700 and 1000 Hz are distorted by a symmetrical compressor alternates with a 400-Hz pointer in the third example. As' a general rule the ear is rather insensitive to the relative phase angles between low-order harmonics of a complex tone. Distortion, however, especially if present in the right amount, can produce noticeable changes in the perceived quality of a complex tone when phase angles are changed. This is shown in the last demonstration in which the phase angle between a 440-Hz fundamental and its 880-Hz second harmonic is varied, first without distortion and with the complex fed through a square-law device.