Q

"Q"

The resonance of an electronic circuit. "Q" actually refers to quality factor. Q is a measure of the sharpness of a resonant peak. The term Q is often used interchangeably with "bandwidth". This is not entirely correct. It is more accurate to say that Q determines bandwidth (a subtle but distinct difference). Q is most often used in reference to synthesizer filters (sometimes referred to as resonance) and equalizers, but it also applies to capacitors (a measure of efficiency, the ratio of capacitive reactance to resistance at a high frequency) and speakers (a measure of directivity). In speakers, a Q of 1 means the system sends out energy equally in all directions; a speaker with a Q of 2 radiates in a 180 degree hemisphere; higher Q's correspond to smaller angles.

Quantization

The division of a continuous event (such as an analog signal) into a series of discrete steps. To quantize or quantify something. In digital audio recording this takes the form of "sampling" (another word for quantizing) the analog signal a specified number of times per second (sampling rate) with each sample made up of some known amount if information (how many bits, or bit depth Ð i.e. 16-bit, 24-bit, etc.). In MIDI it pertains to the timing resolution of a sequencer or drum machine and is measured in Pulses Per Quarter Note (PPQN). For example, a 480 PPQN sequencer has greater timing resolution than a 96 PPQN sequencer. Also in MIDI the verb quantize means to perform an operation to the MIDI data that will bring notes closer to a specified grid of acceptable timing values. For example, you could quantize a performance where someone played inconsistently to make all of their note events land on even quarter notes. Over-quantization results when such correction is so extreme that the resulting sequence becomes stiff or robotic sounding.

Quantization Error

Error resulting from trying to represent a continuous analog signal with discrete, stepped digital data. The problem arises when the analog value being sampled falls between two digital "steps." When this happens, the analog value must be represented by the nearest digital value, resulting in a very slight error. In other words, the difference between the continuous analog waveform, and the stair-stepped digital representation is quantization error. For a sine wave, quantization error will appear as extra harmonics in the signal. For music or program material, the signal is constantly changing and quantization error appears as wideband noise, cleverly referred to as "quantization noise." It is extremely difficult to measure or spec quantization noise, since it only exists when a signal is present.

Quantization error is one reason higher digital resolutions (longer word lengths) and higher sample rates sound better to our ears; the "steps" become finer, reducing quantization errors.

Quasi-Parametric

This term applies to equalizers. A quasi-parametric (also known as "semi-parametric") EQ will allow control over the frequency and gain of each band of equalization, but not bandwidth. The midrange EQs on mixing consoles are often quasi-parametric (sometimes referred to as "sweepable mids"). While more flexible in some ways than a graphic, a quasi-parametric EQ does not offer the "ultimate tweakability" of a fully parametric design.

QuickTime

Developed by Apple Computer, QuickTime is a method of storing sound, graphics, and movie files. It has been in use on the Macintosh for a number of years as the principal video playback technology. Although QuickTime was originally developed for the Macintosh, player software is now available for Windows and other platforms.