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Half-Duplex - the inability to send and receive data simultaneously which, in digital audio terms, translates to the inability to record and play audio at the same time. Many older sound cards are half-duplex. Most modern sound cards are capable of recording and playing audio simultaneously. This capability is called "full-duplex".

Hard disk recorder: A computer-based hardware and software package specifically intended for the recording, manipulation, and reproduction of the digital audio data that resides upon hard diskand/or within the computers own RAM.

Hard Disk: A storage medium for digital data which can hold more information and access it faster than a floppy disk.

Hardware-based sequencer: Stand-alone devices for the sole purpose of MIDI sequencing. These systems make use of a dedicated operating structure, microprocessing system, and memory that is integrated with top- panel controls for performing sequence-specific functions.

Harmful to Minors: Proposals to criminalize the sale to minors of certain sound recordings, sometimes based on the Parental Advisory Label. These proposals threaten the successful Parental Advisory Program the RIAA has had in place since 1985, which in turn would deprive consumers of an important tool for determining the lyrical content of sound recordings.

Harmonic (1) A special case of partial normally occurring in "musical" sounds, in which the frequency of the partial has a simple mathematical relationship to other partials. Generally they are all integer multiples of a particular fundamental frequency. See also Inharmonic. (2) of or pertaining to musical harmony (the juxtaposition of one note with another or others).

Harmonic Distortion: - When harmonics are present in an output signal which weren't a part of the input signal of an audio device, this is referred to as harmonic distortion. The addition of harmonics that were not present in the original signal. The presence of harmonics in the output signal of a device which were not present in the input signal.

HARMONIC SERIES - also known as the ``overtone'' series, this is the series of frequencies in a sound that are whole number multiples of the fundamental.

Harmonic(s): - With the exeption of an electronically generated pure sine wave All of the sounds that we hear gain their essential "character" through the presence of harmonics, which are (in the case of music and audio) soundwaves whose frequency rises in incremental steps from a Fundamental frequency. To use an example, say there was a sound with a fundamental frequency (or if we were being musical, a note or pitch) of 100 Hertz. the "first" harmonic of this would have a frequency that was exactly double this (200Hz), the "second" would be double that (400) and so on. If this were a note, its pitch would corresond to the fundamental frequency of the sound, however the subtle interaction of these higher frequency harmonics of varying amplitudes (levels), will give the sound its "timbre" or "colour". Hence a guitar playing E4 will sound considerably different from a piano playing E4, although the fundamental frequency, or pitch will still be @ 329.63 Hertz (if they are correctly tuned!). Harmonics: A frequency that is a whole-number multiple of the fundamental frequency. For example, if the fundamental frequency of a sound is 440Hz, then the first two harmonics are 880Hz and 1,320Hz (1.32kHz). See Overtone.

Harmony: - As all the musicians will know out there will probably know, harmonic concepts are the primary basis for the contruction of music theory, eg "chords" and the concept of playing music in a "key" are built around the notion of having a fundamental note, with a series of notes higher in pitch than this, their pitches being in harmony with the fundamental note, in line with the harmonic principles mentioned above.

HDR: - Acronym of Hard Disk Recorder. Any digital audio recording device which is based on a computer type hard disk storage device, rather than D.A.T. (Digital Audio Tape), CD etc.

HEAD: The part of a tape machine or disk drive that reads and/or writes data to and from the storage media.

HEADROOM: The safety margin in dBs between the highest peak signal being passed by a piece of equipment and the absolute maximum level the equipment can handle. The difference in dB's or watts etc between the highest level of a sonic signal that is being produced, and the highest level that is capable of being produced without significant distortion/ spontaneous combustion! A sonic system always sounds at it's best when it has lots of headroom, and at its worst when there is no headroom at all, as clipping may result.

Hertz (Hz): A unit of measurement denoting frequency originally measured as one cycle per second (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are Hertz measured in multiples of 1,000. The SI unit of frequency, in particular the number of times something occurs in one second, abbreviated Hz. Named after Heinrich Rudolph Hertz (1857-94). The unit is sometimes alternatively expressed as CPS.

High pass / Low pass / Band pass: A device which allows higher frequency data to be transmitted, rejecting lower frequencies, as used in Graphic EQ’s. For example, your HPF is set at 100Hz. This means everything below 100Hz to 20 Hz will not be as present in your audio signal. If you had a bass drum mic’d, you would not get any low end thump. See Low Pass Filter. (HPF): A filter which attenuates frequencies below its cutoff frequency.High-pass Filter - a type of filter used to eliminate low-range frequencies resulting in a crisper sound, good for creating percussion sounds with distinctive high ranges.

HISS: Noise caused by random electrical fluctuations.

Hologram: Holographic decals depicting the RIAA logo that are placed on certified award plaques and sequentially numbered and registered at RIAA headquarters.

HPF - see High-pass Filter.

HUM: Signal contamination caused by the addition of low frequencies, usually related to the mains power frequency.

Hypercardioid: - see Polar Pattern (cardioid).