Ambiofiles
tools
DIY Ambiophonics
& PanAmbio surround
By
Robin Miller
You
can enjoy free Ambiophonics enhancement of CDs/DVDs/games using your
PC and soundcard or (better) external A-D-A converters. Optionally using
multi-channel converters, expand to 360° surround sound for multi-channel
music, movies, or games (with or without ambience convolution). Choose
either a) Recursive Ambiophonic Crosstalk Eliminator (RACE), which turns
your PC into an Ambiophonic DSP engine, or b) Choueiri multi-band crosstalk
cancellation (BACCH) using convolution. Not "virtual," these
solutions preserve spatial information distorted by crosstalk with ordinary
stereo speakers.
Give
yourself some spatiality; Put a little timbre in your life.
The
intent of audio reproduction is to recreate the perceptions of live
hearing. This implies realistic localization of auditory events, a sense
of immersion within the original acoustic space (spatiality), and above
all timbre, the tone color of voices and instruments. Confining reproduction
to the narrow pie-shape of stereo speakers when in fact we hear a full
sphere of sounds, and introducing crosstalk, distorts these perceptions.
Enter Ambiophonics methods and our passionate international team.
To
audition Ambiophonics for yourself, download these pre-cancelled .wav
files, burn an audio CD, and temporarily reposition L & R speakers
close together (~20° angle to the listener). Using "Width Test,"
move back and forth along a line midway between the speakers until the
image is widest (90~120°) and symmetrical. Play the other excerpts
to demonstrate how recordings have greater realism when reproduced Ambiophonically
than stereophonically (speakers 60° apart). If satisfied, choose
method A or B below for your Ambiophonics media system.
*
Left-Right Width Test (for
positioning, after Setup/Calibration below);
*
Li'l David (small gospel
group a cappella);
*
Handel-Dixit Dominus (large
chorus & orchestra);
*
Parade* (snare drums passing
right to left);
*
Country Style* (workers
at Martin Guitar on lunchbreak).
Intended
for non-commercial experimentation only, these excerpts are from ordinary
releases (except * recorded with an Ambiophone) and pre-processed using
RACE DSP. For a full discussion on RACE see AES
Paper and White Paper.
Also see stereo and surround Modes below. For best
results, calibrate your system first using Setup
below, then verify image width & symmetry using "Width Test"
as above. Ready to DIY?
A:
PC-based Ambiophonics - RACE
w/MIDI
With
help from Angelo Farina and Howard Moscovitz, here is RACE ver.F with
optional real-time MIDI control of 11 operational parameters. Free downloads
of the DSP, AudioMulch host screenshot, and User's Guide are below.
MIDI requires a controller, such as a Behringer
BCR-2000.
Developed
by Ralph Glasgal and Robin Miller, RACE is DSP hosted on a PC to perform
infinite-order crosstalk cancellation, not just first-order found in
others, that recreates the up to 120°-wide stage captured in most
stereo recordings. By turning speakers into virtual headphones for the
best of both speaker and binaural worlds, RACE ver.F needs no head-tracking
- it's like listening live to a concert. Simply with a PC and soundcard,
enhance legacy stereo with Ambiophonics as follows:
*
Download (purchase) & install AudioMulch 1.0 www.audiomulch.com/;
*
Download RACE .amh file here
and open in AudioMulch (picture here);
*
In AudioMulch settings, assign i/o channels for your soundcard, then
press the Enable Audio button. Voilà! Detailed users
guide here.
For
best results, calibrate your system using Setup
below, then verify image width using "Left-Right" test above.
In tests using RACE, expert listeners 200cm from speakers separated
70cm (20°) measured a perceived stage width of 116° for hard-panned
material.
Alternative
if you are equipped for convolution: download
RACE in the form of a 44.1kHz 2x2 impulse response, recorded using Audio
Mulch as above, here.
(Or compare to the TacT RCS2.2XP in mode A-1 using settings 80us and
"75" spread (3dB) as measured here.)
Mac
or Linux users will find free experimental solutions here.
B:
Choueiri Crosstalk Cancellation - BACCH
Ambiophile
Edgar Choueiri, professor of applied physics at Princeton University,
has developed an improved theoretical crosstalk cancellation that is
at the heart of Ambiophonics. Here are tools for doing real-time Choueiri
BACCH crosstalk cancellation using a PC and soundcard or (better) external
A-D-A converters. The same tools can be used to implement a 4-channel
surround system (2 speakers for the front Ambiodipole and 2 for the
back), compatible with 5.1 multi-channel music or movies. Try a front
dipole (i.e. 2 crosstalk-cancelled speakers in the front) before experimenting
with a back Ambiodipole.
BACCH bandsplits L & R signals and optimizes regularization of crosstalk
cancellation of each before recombining with direct signals. The result
yields maximum levels (undistorted headroom) with minimal coloration
from center to sides. Unlike RACE, the listening configuration is fixed
as follows: distance from speakers = 170 cm; speaker separation = 50
cm.
This
implementation uses AudioMulch hosting X-volver multi-channel convolver
(Beta version). Minimum i/o is 2 inputs (stereo) to 2 outputs (front
Ambiodipole). The maximum is 4 in (surround with no center speaker)
to 4 out (Ambiodipoles front & back). Installation steps are:
*
Download and install AudioMulch v1.0 (purchase) from www.audiomulch.com/;
*
Download Farina X-volver .xml
and .zip files to the VST
Plug-ins section of AudioMulch;
*
Download BACCH
ver3 (2x2 .wav file filter for convolution);
*
Download Choueiri.amh
DSP file and open it in AudioMulch;
*
Within AudioMulch settings, assign i/o channels per MODES below for
your soundcard, and press the Enable Audio button;
*
Within one or both X-volver "contraptions," specify "Multi-IR"
mode and IR length of 1024 samples. Load the desired CXC filter. Set
Wet and Dry gains to 0dB and -3dB respectively for comparing filtered
and bypassed signals. Select Wet for the digitally processed Choueiri
Crosstalk Cancellation (not the Mix button).
Prof.
Choueiri sets up to record using Neumann M150s astride a Jecklin-like
disk. A custom CXC filter results in the 1-to-1 correspondence berween
angular locations of original and perceived sources achievable in Ambiophonics.
Ambiophonic
MODES of playback
For
implementations above, the left panel of the AudioMulch interface represents
a block diagram of Ambiophonic digital signal processing (DSP). After
Setup & Calibration below, we suggest progressing through the following
modes, as desired:
1)
AMBIOPHONICS - legacy 2-channel stereo L and R are input to the SoundIn
contraption and Ambiophonics is output from SoundOut and Ambiophonics
CXC is output for a closely-spaced "Ambiodipole" speaker pair.
[Note that precise calibration of individual speaker Sound Pressure
Levels is essential - see Setup & Calibration below - and that all
gain/mixer adjustments in AudioMulch are in pairs so that this balance
and Ambiophonics' fine imaging is not destroyed.]
2)
DOUBLE AMBIO (optional, for stereo input) duplicates the front CXC in
a back Ambiodipole, which widens reproduction even more than normal
Ambiophonics in 1). Set Matrix to route inputs 1 and 2 to outputs 1
and 2 respectively and advance the back level using SGain_2 to taste.
3)
PANAMBIO SURROUND - For 5.1/6.1 music or movies, surround channels SL
and SR are input to AuxIn1 and a second instance of X-volver provides
CXC output via AuxOut1. Set Matrix to route inputs 3,4 to outputs 1,2
as in the illustration above. SGain_1 and SGain_2 adjust the relative
levels of front and back Ambiodipoles. (Be sure to set your player for
"no center speaker" to mix the Center mono channel to the
front Ambiopole for a fine central image.)
4)
SIDE enhancement (experimental, similar to the Beveridge stereo approach,
with speakers 5 & 6 at either side) are non-crosstalk-cancelled
signals, output from AuxOut2, used to widen and uncolor the Ambiophonics
stage to its maximum, approaching 180°. SGain_3 adjusts the relative
contribution of surround input signals. S2Mixer_1 allows easy muting
of the sides and their front/back contributors.
As
you progress in these experiments, controls in AudioMulch enable operating
modes above for (2) duplicating the front signals to a rear dipole for
an even wider stage, (3) processing surround signals to a back Ambiodipole,
and (4) sending unprocessed mix to side speakers (total of six) Beveridge-style
for 180° stereo or 360° surround.
Setup
& Calibration
Ambiophonics
is optimized for one or two listeners on the medial plane of a pair
of front speakers separated only about 50~75cm positioned at ear level
about 2~3m from the listener(s). Choueiri CXC is optimized for separation
of 49.5 cm positioned 1.9 m from the listener(s). Speakers should be
matched pairs, known to have good phase response through any crossover
networks. Correct speaker positioning, avoiding acoustical interference,
and calibrating levels and timing are essential for successful crosstalk
cancellation.
Your ears are the ultimate instruments of perceived quality. But first,
calibrate speaker SPL using an SPL meter ($30 at Radio Shack) and this
link to band-limited pink noise.
Burn this file, the Left-Right
Width Test, and any desired demonstration files above to an audio
CD. With no crosstalk cancellation processing, the player set for loop
repeat of the pink noise, and SPL meter fixed at the listening position,
adjust each channel individually using level controls at the power amplifier
inputs so that the signal (-18dB below digital Full Scale) produces
precisely 85dB SPL from each speaker individually.
Still
with no crosstalk cancellation processing, play pre-cancelled music
excerpts above to verify speaker and listener positioning. Now with
crosstalk cancellation processing, play pink noise through only the
left input of the system and, if necessary, adjust speaker separation
slightly relative to a fixed listening position so that at the listening
position the sound is perceived at the extreme left only. Repeat iteratively
using the right input only (for extreme right perception) until the
widest stage width is achieved, up to 120° - double stereo's 60°
- but with none of stereo's "hole in the middle" or distortion
of tone color, especially for important central sounds.
If a 90+° symmetrical image is not achieved, something is wrong
- most likely acoustic interference or a phase problem - either speaker
wiring or crossover inequality between speakers. Listening
space acoustics are important and can destroy crosstalk cancellation.
To reduce room interference, even without recourse to acoustic absorption
material, speakers should be positioned at least 8ft (2.5m) from walls
or other reflectors and as symmetrically within the room as possible.
If acoustics are changed or anything is moved, levels should be recalibrated
as above using only the power amplifier inputs, as all levels remain
balanced through the Ambiophonics DSP.
About
these tools
While
these implementations have been tested at the Ambiophonics Institute
and at FilmakerTechnology using commonly available PCs and audio converters,
we can offer no warranty or customer support. It is assumed that you
have moderate proficiency with a PC and audio equipment - and good ears!
Downloads on this page are only for personal use to enjoy either stereo
recordings (results vary with the recording technique) or 4.1/5.1/6.1
multi-channel audio or movies (setting your player for "no center
speaker"). We leave judging the results to you, but if all is well,
you will hear Ambiophonics' artifact-free wide (120+°) front stage
or 360° surround, as described throughout this website. R&D
is ongoing, so revisit, as tools and demonstrations are posted as soon
as available.
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