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Glossary of Terms

Bandwidth
The range of frequencies that has been specified as performance limits for an audio component. Defined as between the -3dB (half power) points at the high-pass and low-pass ends of the frequency response. In high-performance audio equipment, these limits range from about 3Hz to at least 50kHz.

Bipolar Transistor (BJT)
A bipolar junction transistor (BJT) is a type of transistor, an amplifying or switching device constructed of doped semiconductors that employs both types of charge carriers: electrons and holes. The BJT is a three layer sandwich of differently doped sections, either NPN transistors or PNP transistors.

Class A
A type of output stage biased so that all of the output devices remain in their active region at all times.

Class A-B
A type of output stage biased so that each output device (there must be at least two) will only conduct or remain active in excess of 180 degrees of the Alternating Current (AC) cycle. Essentially the same as Class B but over biased to some extent.

Class B
A type of output stage biased so that each output device (there must be at least two) will only conduct for one-half of the Alternating Current (AC) cycle (approximately 180 degrees).

Clipping - Soft and Hard
Clipping is the distortion that occurs when an amplifier or pre-amplifier is overdriven. This can be seen visually on an oscilloscope as the peaks of a waveform are flattened or "clipped off" at the signal's ceiling. Clipping may be hard, as is the case when the signal is strictly limited at some level; or it may be soft, in which case the clipping signal continues to follow the input at some reduced gain.

Damping Factor
The ratio of the output impedance of a power amplifier output stage and the impedance of a speaker system.

Discrete
A general term used to describe circuitry that does not contain integrated circuits. In other words, circuits constructed from individual resistors, diodes, transistors, and so on.

Fast Fourier Transform
The Fast Fourier Transform (FFT) is a very efficient computer algorithm designed to calculate the frequency components of sounds and other signals. A computationally efficient mathematical technique which converts digital information from the time domain to the frequency domain for rapid spectral analysis.

Harmonics
Frequency component at a frequency that is an integer multiple of the fundamental frequency. A weaker overtone or undertone of the original note responsible for the character of the note. A single frequency component of a sound. An integral multiple or sub-multiple of a given frequency; a sinusoidal component of a periodic wave. Also called "overtone," or "partial." The timbre, or tone color, of a sound may be characterized by its harmonic content.

• Even-order harmonics are harmonics that occur in even multiples of the fundamental. For example, a 1kHz tone will have harmonics at 2kHz, 4kHz, 6kHz and so on.
• Odd-order harmonics are harmonics that occur in odd multiples of the fundamental. For example, a 1kHz tone will have harmonics at 3kHz, 5kHz, 7kHz and so on.

Lateral MOSFET
A planar type of MOSFET (in contrast to the V-groove double-diffused MOSFETs commonly referred to as V-MOSFETs, HEXFETS, or D-MOSFETS) Lateral MOSFETs were designed specifically for audio applications and have significant advantages over vertical MOSFETs for audio power amplifier applications. Lateral MOSFETs also cost considerably more (up to 10 times) than common V-MOSFETs. Understandably, Lateral MOSFETs are rarely found in audio amplifiers due to their extremely high cost. However, for ultimate sonic performance the Lateral MOSFETs are unparalleled.

% Total Harmonic Distortion + Noise (%THD+N)
A condition in which a circuit adds additional unwanted harmonics (e.g., second and third harmonics) that were not part of the original signal. THD represents the effect of all the harmonic components (hence the "total" part of the name, as opposed to second- or fifth-harmonic distortion) and is usually expressed as a percentage of the output signal. Since the primary method of THD extraction will include whatever noise characteristics are inherent to the amplifier or pre-amplifier under test, the technically accurate way of expressing THD measurement is "percent THD+N" (the N stands for noise).