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Ambiophonics
2nd Edition
Introduction
Preface
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Appendix A

Figures
>Figure 1
>Figure 2
>Figure 3
>Figure 4
>Figure 5

University of York Ph.D. researcher Alastair Howe Moore heard Ambiophonics while at AES123 presenting a paper on binaural audio and HRTF accuracy in externalizing auditory images (AES preprint #7166). For Ambiophiles with Mac or Linux computers to experiment, he has posted a free algorithm patch using pure data and a convenient 'container' patch. To download, go to www-users.york.ac.uk/~ahm105 and click on the "Ambiophonics" link.

[NOTE: Neither Ambiophonics Institute nor FilmakerTechnology has tested these Mac and Linux solutions, so we cannot verify them at this time. However, anyone wanting to conduct an experiment and share an opinion may download a 44.1kHz 16bit test Dirac and e-mail the recorded impulse response as a .wav file to enquire@filmaker.com for analysis.]

In Parma, a RAVE for RACE and BACCH

Ambiophiles are growing in number around the world. After attending the AES Italia 2007 in Parma, Italy, invited panelist David Malham of the University of York wrote to the Sursound List: "I participated in the listening tests at Parma and was really impressed with how far this technology has gotten - it's well worth a try. Particularly for domestic listeners who only have stereo material, it certainly does what it says on the can. I think I marginally preferred RACE on some material and the BACCH on other." [Note: BACCH ver1 demonstrated in Parma has since been much-improved as BACCH ver3, downloadable here along with RACE for PCs.]

Raves for Tact RCS-2.2XP with Ambiophonics DSP

In an open letter to stereophiles, Michael Graw of Luebeck, Germany, wrote: "I had the chance to listen to a TacT 2.2 XP with its [Ambiophonic] cross talk cancellation (XTC) function activated and must admit: It really works even in a normal stereo loudspeaker arrangement. The [Ambiophonic] XTC is the biggest improvement I could experience in my 35 years of optimization of my system and searching for a true high fidelity system."

Dr. Radomir "Boz" Bozovic of Tact Audio demonstrated the room correcting RCS-2.2XP containing 10 adjustable Ambiophonic algorithms at CES and, above, to the New York Audiophile Society at the Ambiophonics Institute.

TacT Audio's RCS-2.2XP software update is available for downloading (www.tactlab.com) and includes Ambiophonics crosstalk cancellation algorithms. Accessed via an additional menu called " XTC" that can be turned ON or OFF at any time, use this option to experience realistic binaural-like sound reproduction.

What is crosstalk cancellation? When you listen to your stereo system, the left channel signal intended for the left ear also reaches right ear and the right channel signal reaches left ear, producing the cross-talk effect. This acoustic crosstalk adds false time-domain information and disables localization cues. Crosstalk can be eliminated (reduced) using a digital signal processing (DSP) technique known as cross-talk cancellation (XTC). Acting like virtual headphones, XTC's purpose is that the left channel signal is delivered to the left ear only, and the right channel signal is delivered to the right ear only.

The TacT RCS-2.2XP implements two sets of five XTC algorithms with parameters adjustable by the user in real time. In total there are ten different user selectable RACE (Recursive Ambiophonic Crosstalk Eliminator) algorithms, developed by Ralph Glasgal and Robin Miller. Selection of algorithm and adjustment of their recursive parameters allow the user control of the perspective of legacy stereo recordings, most of which contain usable imaging information that would be distorted by crosstalk using normal stereo speaker placement.

Achieved by relocating the speakers closer together, the Ambiophonic method using the RACE modes can sound dramatic, creating image stages up to 150° wide with some CDs, as one would hear if one were at the main microphone positioned above the conductor's podium in a concert hall, or in front of the lead singer in rock group. For a string quartet that might naturally be 50° wide, varying XTC parameters with the TacT RCS-2.2XP provides that perspective, or can relocate the perspective to, for example, the fifth or tenth row center. First-time listeners to Ambiophonics are often astounded that the imaging is "inside-out," with sounds presented with correct timbre and localization all across the front stage, well beyond the speakers, and not merely between them as with stereo phantom imaging.

Simply put, the ten modes available in the Tact pre-pro vary the ratio of the bandwidth processed for crosstalk cancellation to the bandwidth of most of the sound, which is totally unprocessed. When the combination reaches the listener's ears, the processed signals disappear, along with the acoustic crosstalk. In each of two sets of five algorithms, A-2 through A-5 increases the XTC bandpass (both high and low frequencies) restriction, while B-2 through B-5 increases only low frequency restriction, with A-1 an B-1 offering the widest stage with no restriction. Increasing restriction avoids artifacts due to comb filtering.

In any one of the ten modes, tweaking the parameters of recursive delay and "spread" (recursive attenuation) allows adjustment for recordings with high differences in interaural level and time, or compensate for those with unusually low interaural differences, thus achieving a greater sense of realism - of being there. Generally, recursive delay allows the user either a more focused or a looser sweet spot. "Spread" (recursive attenuation) varies the stage from very narrow to very wide, or anywhere in between.

To experience Ambiophonic reproduction using the Tact RCS-2.2XP, position two loudspeakers at an angle of approximately 20° instead of stereo's usual 60°. Refer to www.ambiophonics.org for more Ambiophonic theory, loudspeaker placement diagrams, and DIY tools for Ambiophonic DSP with fixed parameters suitable for most stereo source material.

Ralph Glasgal hosts the New York Audiophile Society at the Ambiophonics Institute, where 40 attendees heard the new TacT RCS 2.2XP process both stereo and surround recordings using Ambiophonic algorithms.

 Tools to build your own Ambiophonic or PanAmbio 4.1 surround system