Downmixing

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Downmixing is a general term used for manipulating audio where a number of distinct audio channels are mixed to produce a lower number of channels. It is also known as fold-down.

Sometimes, "Downmixing" is also used in radio communication to describe a process that brings an IF signal down to baseband via demodulation with a complex carrier frequency.

Example[edit]

Many DVD players and Personal computer sound cards can downmix multichannel audio (e.g. 5.1 surround sound) to stereophonic sound (2 channels) for output via two speakers.

Stereo downmixes/(or fold-downs)[edit]

Left total/Right total (Lt/Rt)[edit]

Lt/Rt is a downmix suitable for decoding with a Dolby Pro Logic decoder to obtain 5.1 channels again. Lt/Rt is also suitable for stereophonic sound playback on a hi-fi or on headphones as it is.

Lt = L + -3dB*C + -3dB*(-Ls -Rs)

Rt = R + -3dB*C + -3dB*(Ls + Rs)

(where Ls and Rs are phase shifted 90°)[1]

Left only/Right only (Lo/Ro)[edit]

Lo/Ro is a downmix suitable when mono compatibility is required. Lo/Ro destroys front/rear channel separation information and thus a Dolby Pro Logic upmixer will not be able to properly extract 5.1 channels again.

Lo = L + -3dB*C + att*Ls

Ro = R + -3dB*C + att*Rs

(where att = -3dB, -6dB, -9dB or 0)

See also[edit]

References[edit]