Overtones are those frequencies of a musical sound that are multiples of the fundamental (generally the lowest frequency in a complex tone). The harmonic that is twice the fundamental frequency is called the second harmonic: three times the fundamental, third harmonic and so on. Each instrument, including the human voice, has a particular harmonic overtone "structure" that is a key factor in making the sound of the instrument identifiable and distinguishable from other instruments. When we refer to the audible musical frequency range as extending beyond 15,000 Hz, we mean that some instruments have significant overtones that reach that high, al though their fundamentals are considerably lower.
Pan pot ("pan" being short for panoramic, "pot" for potentiometer) is a control usually found on elaborate mixers. It distributes an audio signal be tween two or more channels in much the same way the balance control on a stereo amplifier can be used to position a mono phonic signal anywhere between the two speakers. During multitrack recording work (in which each instrument is as signed its own tape track), the recording engineer can adjust the final position of each instrument in the stereo spread by manipulating pan pots in advance and then mixing down the multitrack tape into two or four channels. He can also cause instruments to shift in location during a musical selection by manipulating the pan pots while the mixdown is taking place. Peak is the term for an amplitude maximum, the point(s) at which the waveform of a signal deviates most from the "zero" axis around which it is evolving. Naturally, the incidence of a peak in a musical waveform corresponds to a loud passage, or, more properly, to the very loudest instant of a loud passage. Peaks in recorded music are quite often 10 dB or so above the overall "average" level, and they may go considerably higher, depending on what type of music it is and whether an effort has been made to preserve the full value of the peaks. These peaks represent moments of very high power demand on an audio system. As a rule, they are of very brief duration-so brief, in fact, that the most severe ones can frequently be eliminated in the recording studio (by a process called "peak limiting") with little or no audible effect on the program. The object of such limiting is usually to make the program easier to record and play.
For many years some manufacturers of sound equipment (usually not the most highly esteemed of such manufacturers!) rated their amplifiers in terms of "peak power" or some variant thereof such as "instantaneous peak power." This rating system did not refer to the instantaneous signal peaks, but was in stead a mathematical manipulation whose only purpose was to inflate the power rating. "Peak" power ratings of this sort should not be confused with dynamic or music-power ratings.
Phase refers to the relationship in time of two waveforms or of the different components of a single complex wave. This time relationship may be calibrated in actual time units such as milliseconds, or in phase angles, with each 360-degree interval containing a full cycle of the waveform.
The concept of phase really has meaning only when distinct waveforms (such as input and output) can be compared to determine the degree to which they are "in phase" or "out of phase." An out-of-phase condition implies that one or more of the waveforms has undergone a time displacement or phase shift (calibrated in degrees) that has taken it out of synchronization with the other(s). Phase shift can also occur within a single wave form, as when some frequencies of a complex signal are displaced in time relative to others. A square wave, for example, will undergo radical changes in shape if passed through an amplifier which has a different amount of phase shift at different frequencies.
Most components in an audio system introduce some phase shift, including loudspeakers, tape machines, phono car ridges, and various circuits in amplifiers. However, the importance of absolute phase integrity is a controversial issue. For example, it is known that out-of-phase speaker systems can upset the listener's ability to localize sounds below about 2,000 Hz and produce destructive interference (cancellation) of low-frequency sounds within the listening room.
It is also obvious that phase errors in stereo FM tuners or four-channel matrix decoders can adversely affect their operation. Nevertheless, there is still little agreement on the audibility of the more complex phase shifts between the various drivers of a multi-way speaker sys em, or the importance of maintaining absolute phase integrity in amplifiers.
Phasing means observing a uniform scheme of polarity between channels when interconnecting audio components. In simpler terms, if terminal one of a speaker system is connected to the "+" output of a stereo amplifier and terminal two to the "-" or "common" out put, any other speakers should be hooked up to their amplifier outputs in he same manner. This will ensure that the diaphragms of the speakers move in he same direction (that is, in phase) when they are reproducing signals common to all of them. This prevents serious cancellation of low-frequency sounds and other effects of phase anomalies.
All the components in an audio system should have their channels "phased." This is easy to insure with components using phono-jack connectors: polarity is determined by the way in which the jacks and plugs mesh, and it cannot be reversed accidentally. However, the rules of phasing must be observed care fully when installing speaker systems and phono cartridges, since these components permit ready interchanging of leads. (Fortunately, instruction manuals for these devices are generally quite explicit about polarities and phasing requirements.) A pitfall less easy to avoid involves components of different make-microphones, for example, or even different brands of speakers-that do not conform to any polarity standard in the wiring of their connectors. With these it is sometimes necessary to experiment, trying them both ways (by interchanging the leads of one of them) to determine which mode of connection gives the fullest bass response. In the recording studio, "phasing" has lately acquired an additional meaning: a mixing technique in which phase interference between signals being mixed is deliberately introduced, creating a strange, surreal sonic effect.
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Also see:
THE SIMELS REPORT, STEVE SIMELS
CHOOSING SIDES, IRVING KOLODIN