BACCH-Stratos

7.1.4 Surround

emulation

from only two loudspeakers.

Replicate your

best high-end loudspeaker

into 12 virtual

copies placed

around you,

and render

surround sound

in up to 7.1.4 channels

"I [...] watched current TV shows

and first-run movies

with Stratos operating,

and the audio was 95% as effective

as with the average

home-theater setup"

Andrew Quint, the Absolute Sound, January 2026 Issue

BACCH-Stratosonic (BACCH-Stratos) is an advanced spatial-audio technology available as an optional module for the BACCH4Mac system from Theoretica, the creator of the multiple award-winning BACCH®3D Sound technology . BACCH-Stratos was developed by Professor Edgar Choueiri of Princeton University, recipient of The Absolute Sound Innovator of the Year (2025) award.

BACCH-Stratos enables audiophiles to replicate a reference loudspeaker into up to twelve virtual copies, positioned around the listener to reproduce standard 7.1.4 surround-sound layouts using only two physical loudspeakers.

BACCH-Stratos does not decode Dolby Atmos® content. Instead, BACCH-Stratos accepts up to twelve discrete PCM audio channels that have already been decoded on the Mac by a Dolby-licensed playback application. Supported sources include Apple Music® and Apple TV®, as well as the Dolby Reference Player, which can play lossless Dolby Atmos audio and video files.

By combining Dolby-licensed decoding with BACCH-Stratos rendering, listeners can enjoy immersive surround music and films as their creators intended—without the cost, complexity, or physical intrusion of multiple loudspeakers, multi-channel DACs, and amplifiers.

(Dolby Atmos® is a trademark of Dolby Laboratories Licensing Corporation. Apple®, Apple Music®, Apple TV®, and macOS® are trademarks of Apple Inc., registered in the U.S. and other countries.)

Individualized Calibration

BACCH-Stratos relies on a calibration sequence of seven guided binaural acoustic measurements, which take approximately five minutes to complete. These measurements are performed using Theoretica’s BACCH-BM in-ear microphone, a scientific-grade, individually calibrated device with an ultra-linear frequency response, worn by the listener seated in front of two reference loudspeakers.

During the measurement process, the listener is
instructed to move the head in seven defined directions. These measurements capture the acoustic signature of the reference loudspeakers as if the loudspeakers were positioned at the locations prescribed by standard ITU surround-sound configurations.

The resulting binaural data enable the software to compute a set of high-resolution digital (Stratos) filters that reproduce, at the listener’s ears, the spatial cues required for the ear–brain system to perceive each audio channel as originating from a corresponding virtual replica of the reference loudspeaker, placed in the specified standard configuration.

Head Tracking

BACCH-Stratos relies on BACCH 3D Sound to project virtual loudpeakers in three-dimensional space. The resulting spatial image is made highly robust to head movement through continuous tracking of the listener’s head at a temporal resolution of 16 frames per second and a spatial resolution of 1 mm, with real-time updates of the BACCH filters. Head tracking may be performed using an optional optical webcam or an infrared sensor, enabling accurate operation in low-light environments or complete darkness.

When used in conjunction with Theoretica’s Optimal Room Correction technology (BACCH-ORC), the same head-tracking data are used to update the BACCH-ORC filters in real time, ensuring that Stratos’s three-dimensional projection of the virtual loudspeakers and the room-correction processing remain perfectly matched and continuously synchronized with the listener’s head movements. (Head tracking may be optionally disabled if the listener does not intend to move beyond the primary listening position.)

Features & Requirements

BACCH-Stratos is currently available as an optional module for BACCH-dSP 15 , the core application of Theoretica’s BACCH4Mac system. (It is availbale only for the Audiophile edition of BACCH4Mac, and higher editions.) BACCH-dSP 15 requires a Mac with an M1 processor or later, running macOS up to the current version 26 (Tahoe), and equipped with a minimum of 16 GB of RAM.

BACCH-Stratos, like BACCH-ORC, is supplied with default presets that are optimal for most listening environments. Advanced settings and built-in diagnostics allow the Stratos filters to be fine-tuned for specific cases when required. Theoretica provides full technical support to users with a valid one-year BACCH4Mac Service Plan, including an individualized remote Stratos walkthrough session to assist with setup, demonstrate its straightforward operation, and, when necessary, optimize its settings.

Rendering 5.1 surround sound requires a minimum XTC level of 6 dB, as computed by the BACCH-dSP application from the acoustic measurements. This requirement is readily met in most listening rooms. For more robust rendering of the rear surround and height channels in 7.1.4 content, an XTC level above 8 dB may be required.

Stratos emulation operates within a defined sweet spot for the primary listener, approximately 8 inches square. This sweet spot can be significantly expanded laterally through the use of built-in head tracking. Listeners positioned outside the sweet spot will not experience a full emulation of the surround loudspeakers.