Enhanced Stereo filters mix part of the direct sound across channels, using a “matrix”. One part of the filter affects the direct sound in each channel. A second part of the filter feeds from left to right, and symmetrically from right to left.
This can be used for some interesting and useful things:
- To increase spatial separation between channels. The various “Space” filters broaden the stereo image in a normal system to well beyond the loudspeaker positions, enhancing the “they are here” feeling. This is wonderful with simply-recorded live music.
- To support the Ambiophonics “AmbioDipole” arrangement, where the loudspeakers are positioned close together yet you hear a realistic sound stage encompassing upward of 120 degrees.
- For headphone listening, using various sorts of cross-feed to move sounds “outside the head” into a more realistic presentation.
- For loudspeaker listening to binaural recordings.
- To add simulated concert-hall ambience, for a very realistic “you are there” experience.
Installing Filters
Enhanced Stereo filters should be copied to the “MatrixImpulses” folder.
- On Windows, this is .
- On Windows Vista, this is .
- On linux, this is in .
The “Enhanced Stereo…” plugin menu lists all WAV files it finds in this folder.
Examples
- Headphone crossfeed: Headphone1, Headphone2
- Headphone crossfeed with added room ambience: Headphone3
- Binaural recordings made with Neumann head: Binaural1, Binaural2 (from Angelo Farina’s data)
- Ambiophonic stereo dipole: ChoueiriStereoDipole (original by Edgar Choueiri of Princeton; via Angelo Farina)
Selecting a Filter
Using the remote control, browse to the plugin menu
This shows a list of all the stereo crossfeed filters: these are all the WAV files found in the folder, and “None” to select no crossfeed processing.
Push right to select a filter file. The selected stereo filter will take effect on the next track played.
Technical Details
These filters are two-channel impulses in a stereo WAV file format. (32-bit IEEE float is preferred, but all PCM WAV formats are supported). The filters can be as long as necessary, at the expense of processing speed. For most purposes they should be less than about 4000 samples. A sensible practical limit for most users’ PCs is around 32000 samples (which should be enough for even the most intense ambience simulations).
These matrix filters are always symmetrical (left-right crossfeed is processed with the same filter as right-left). So, unlike the sample files on the Ambiophonics site, these filters only include one left/right impulse pair. They are applied before room-correction filters (i.e. the output of the matrix filter is fed through the room-processing filter).
The left channel of the filter file is an impulse to be convolved with the direct channels (left to left, and right to right). Usually this should be close to a Dirac pulse (because with most filter effects you don’t want to affect the direct sound much), but it can be any impulse for FIR convolution.
The right channel of the filter file is an impulse to be cross-fed between channels. The left channel is convolved with this impulse and the result added to the right output. Simultaneously, the right channel is convolved with the same impulse and the result added to the left output.
Matrix filters should be built with the most commonly-used sampling rate (e.g. 44100 for CD material). But they can use any sampling rate, and will automatically be rescaled (using sox polyphase) to the playback rate as necessary.
