Crossfeed is the process of blending the left and right channels of a

stereo Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configurat ...

audio recording. It is generally used to reduce the extreme channel separation often featured in early stereo recordings (e.g., where instruments are panned entirely on one side or the other), or to make audio played through headphones sound more natural, as when listening to a pair of external speakers. Crossfeed is claimed to provide relief for a small fraction of listeners who otherwise complain of "fatigue" and headaches when they listen to stereo recordings. Crossfeed is most commonly found in

headphone amplifier A headphone amplifier is a low-powered audio amplifier designed particularly to drive headphones worn on or in the ears, instead of loudspeakers in speaker enclosures. Most commonly, headphone amplifiers are found embedded in electronic devices t ...

s and often can be toggled with a switch. Many audio player programs for computers can perform crossfeed via plug-ins or built-in processing.

Principle of operation

Directional sound perception is based on the delay between the same sound reaching a person's left and right ears. In stereo speakers, the sound from one speaker reaches both ears, although at different levels, and with a delay between one ear and another, since the speaker is placed away from the center. In headphones, this ''crossfeed'' does not occur, so the resulting stereo image is different from what is heard from speakers. A crossfeed signal processor attempts to recreate the stereo image heard from speakers by mixing some signal from the left channel into the right channel, and vice versa. The intent to produce speaker-like sound in headphones distinguishes crossfeed from the more general concept of stereo width reduction, which involves similar techniques.

Types of crossfeeds

Analog

An analog crossfeed is usually implemented by mixing the left and right channels together to some extent. Since such crossfeeds do not typically correct the delay between the added information and the original signal, they simply reduce the amount of stereo information available, centering the image in the stereo field.

Digital (DSP)

A digital, or DSP-type, crossfeed is typically more sophisticated, mixing an amount of signal from one channel to the other, delaying the signal to mimic

interaural time difference The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the Sound localization, localization of sounds, as it provides a cue to the direction or ...

s and applying other characteristics of

head-related transfer function A head-related transfer function (HRTF) is a response that characterizes how an ear receives a sound from a point in space. As sound strikes the listener, the size and shape of the head, ears, ear canal, density of the head, size and shape of n ...

s (HRTFs) to mimic the changes between the left and right ears. Some digital crossfeeds include controls for varying the realism of the crossfeed implementation and which HRTF characteristics are used. Examples of DSP crossfeeds are

Dolby Headphone Dolby Headphone is a technology developed by Lake Technology (Australia), that later sold marketing rights to Dolby Laboratories, sometimes referred to as Mobile Surround, which creates a virtual surround sound environment in real-time using any ...

and Bauer stereophonic-to-binaural DSP.

References

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External links