H

Haas Effect

At Sweetwater Sound this is the phenomenon that occurs when our Director of Human Resources, Kristine Haas, enters a room carrying pink slips. The more commonly known usage of the term is in audio and pertains to the psychoacoustic phenomenon of sound source localization. If a sound source is presented to our ears at the same level, but one arrives just a few milliseconds later, our hearing mechanism will judge the sound to be coming from the side of the head where the earliest sound arrived. How far to one side or the other depends on the difference in time between the sound arriving at each ear. This is true for arriving sounds up to about 25 milliseconds of delay, after which it will begin to sound like two distinct sounds. This phenomenon is used in all kinds of audio production techniques to help position various instruments around the stereo (or three-dimensional) soundfield without creating imbalances in the levels of the left versus right signals.

The effect is also called the precedence effect and means that if there are two sources of sound, as is often the case with PA systems or studio monitoring systems, the sound will be localized to the speaker that provides the earliest sound. The other speaker will not be heard at all it some cases.

Half Normal

In patch bay jargon this refers to a normal that is only broken by inserting a plug into one of two plugs that are normalled together. In typical patch bay design the top jack of any pair is usually not affected by having a plug inserted into it. It will still route signal down to its lower counterpart. When a jack is inserted into the lower plug, however, the normal connection is broken. This provides a convenient way to route signals to multiple destinations. For example, the output of a mixer that is normalled to the input of a DAT on the patch bay can also be simultaneously routed to another patch point. To do this one would simply run a patch cable from the patch point that is the output of the mixer (an upper jack) to the patch point that is the input to the other device (a lower jack). This connection will break the normal of what would normally be feeding that other device in favor of the mixer signal that has been patched in. Signal will now be routed to the DAT and the other device.

Half-Track

An analog tape head configuration for two track recording. Half-track heads are designed to record two tracks, each on half of the recording tape. Unlike consumer based recorders, which are often quarter track configurations (two each direction), half-track machines can only record the tape in one direction. The idea is to maximize the available tape surface for the two audio (L & R) tracks for best sound quality.

Handling Noise

A specification for quantifying the sensitivity of a microphone to movement and shock. Handling noise is expressed as an equivalent sound pressure level as is a function of the construction of the microphone. This is an often overlooked concern when choosing a microphone as there can be vast differences in handling noise between two otherwise similar mics. Some manufacturers actually employ internal shock mounting devices to reduce handling noise.

Hangover

In the domain of sound reproduction (as opposed to inebriation), hangover is the tendency of a loudspeaker cone to continue moving after reproducing a sound, or especially, a transient (see WFTD archive transient). This is both a low frequency and high frequency phenomenon, and can only be reduced by adding damping to the system. One way of doing this is to increase the damping factor (see WFTD archive damping factor) of the amplifier.

Harmonic Distortion

Since no electronic device is perfectly linear (meaning the output exactly equals the input) harmonic distortion is a fact of life in all audio components. Most audio signals have harmonics associated with them (a perfect sine wave is one notable exception), and that is what gives them their characteristic sound. An oboe sounds different from a violin mostly because of the harmonic series produced as part of their distinct sounds. The corresponding difference in the shape of their respective waveforms is easily distinguished when viewed on an oscilloscope or a computer audio editing program. Harmonic distortion is the result of a device subtly, or not so subtly, changing the shape of the waveform which alters the relative levels of various harmonics associated with that sound. The more harmonic distortion there is the more the sound will begin to take on the quality we all know and love that we call "distorted".

In spec land you will often see the specification for THD which stands for Total Harmonic Distortion. This is a rating given to most gear for the overall percentage of harmonic distortion added to the signal passing through the device while operating at (presumably) nominal levels. There are dozens of ways to measure this spec that can skew the results so keep that in mind when comparing product literature.

HDCD

Abbreviation for High Definition Compatible Disc. This is a new format for high-resolution audio on regular five-inch (CD) style discs. Basically they are just like a regular CD, except they have 20-bit (as opposed to the traditional 16-bit) audio recorded on them. While discs made to this standard are (thankfully) compatible with existing 16-bit CD players, it takes a special HDCD player to reproduce the full 20-bit audio.

Headroom

The difference between the normal operating level of a device, and the maximum level that device can pass without distortion. Music generally has wide variations in dynamic range; without enough headroom, you'll find your gear clipping (distorting) far too frequently! There are a variety of other places where it is desirable to have large amounts of headroom (i.e. when mixing signals together); in general the more the better!

Heat Sink

An structure used to dissipate heat in devices that are prone to produce heat faster than they can dissipate it themselves. For example: The transistors in a power amplifier have very large amounts of current running through them and can get quite hot. Because they are relatively small the heat cannot dissipate very quickly and can cause failures. As a remedy they are mounted to a heat sink (usually aluminum) that is designed to have much more surface area in contact with the air. Often these heat sinks can be seen on the back of amplifiers and big power supplies as an array of metal "fins." Some designs employ fans that circulate cooler air over the hot heat sink to further enhance its ability to pull heat away from the components.

Hertz

Abbreviated Hz, and named for Heinrich Hertz, a 19th-century German physicist who first investigate radio waves. Hertz is technically defined as the inverse of the time required for one complete cycle of a wave. Thus, a 10 Hz sine wave takes 1/10 of a second to complete a full cycle. In practice, it is the frequency or number of wave cycles occurring per second. In the audio range this equates to what we perceive as pitch.

HFS (& HFS+)

Abbreviation for Hierarchical File System as is used by the Macintosh computer system for hard disk data organization. HFS has been used by the Macintosh since about 1986 and is still in widespread use today. Recently Apple has introduced an updated architecture they are calling HFS+. HFS+ addresses a variety of shortcomings in the old HFS, including the ability to handle files over 2 gig in size, allowing names up to 255 characters long, using more of the available hard disk space and packing the data more tightly on the drive, thus conserving space.

Hot Swap

A descriptive phrase that refers to the removal and/or insertion of a device in a system while power is applied. In most electronic equipment it is only safe to change components or sub assemblies when the unit, or any other attached equipment, is off. In some instances, however, a device is designed specifically so a part of it can be removed while it is on. One example of this would be a SCSI drive that is part of an assembly where the drive mechanism can be removed, and another inserted, while power is on. This is called "hot swapping" the drives, and is a feature that many busy studios are willing to pay top dollar for because the alternative is shutting down the whole system to change out a drive.

House Sync

See Video Sync

HX Pro

A circuit employed by many modern analog tape recorders to improve recording quality. Developed by Dolby Laboratories, HX Pro varies the bias signal (see WFTD archive Bias) in record mode to reduce the tendency toward self-erasure. In magnetic tape recording, loud high frequencies in the signal can sometimes look like bias to the tape and will tend to erase the signal as it is being recorded. The effect is called high frequency compression and is a fault of magnetic recorders in general and cassette recorders in particular. The HX Pro system senses the level of high frequencies and reduces the level of bias accordingly. Because it is made by Dolby Labs and bears the Dolby trademark many users think it is a form of noise reduction since that is what Dolby has been most known for. It is not noise reduction, and does not require a "decode" process like typical noise reduction schemes (Dolby included) and is only applied during recording. The benefit of HX Pro is increased headroom during recording, especially with high frequencies. HX Pro recorded tapes play back just fine on any tape machine.

Hypercardioid

A polar pattern name typically used to describe microphone pick up characteristics. Hypercardioid patterns are similar to cardioid patterns in that the primary sensitivity is in the front of the microphone. They differ, however, in that the point of least sensitivity is at the 150 - 160 and 200 - 210 degree positions (as opposed to directly behind the microphone in a cardioid pattern). Hypercardioid microphones are thus considered even more directional than cardioid microphones because they have less sensitivity at their sides and only slightly more directly behind. Hypercardioid microphones are frequently used in situations where a lot of isolation is desired between sound sources.

Hysteresis

In almost any mechanical, magnetic or electronic system, the system's response to rising input is different from its response to falling input. This is obviously an important factor in the response of a recorder or other audio component - you want both the positive and negative parts of the waveform represented accurately! This is part of the reason for things like bias on tape recorders...