As long as we have a person from Theoretica following this thread, I have a question regarding the Pro Edition of Bacch4Mac.
Adam, I see the Pro Edition appears to have three features the Audiophile+ and Audiophile editions lack. Specifically, I would like to know about what the Bacch 3DM, and Bacch-hoa. Who and what are they for? Would an ordinary audiophile who simply wants to use Bacch to play back music and cinema have any use for them? It looks to me like they could be of use in downmixing Atmos program material to a binaural simulation in real time to play over speakers or headphones. Is this correct, and does it work, like say a Smyth A16 which provides this for headphones? And does the B4M extend this capability to two channel speaker systems as well? Would this work, for example, if I wanted to play a Netflix Atmos movie streamed on my Mac Mini, and have my two channel set up realistically emulate 24 channel Atmos? Could Bacch even get the Atmos LPCM stream from the MacMini? And would it not need LPCM because, I'm sure, Bacch doesn't come with an Atmos license?
Or am I just misreading this, and are these features rather designed to be useful to content creators, more so than regular audiophiles?
Both the hoa and 3dm modules, which as you stated correctly are only available in the Pro Edition of BACCH4Mac, are described on the
BACCH-dSP webpage. Basically, the hoa module features many advanced technologies for higher order ambisonics (HOA) to binaural downmixing, sound field navigation, beamforming, head-tracked beam steering, stereo microphone emulation, etc. that are not (yet) of direct relevance to audiophiles. The BACCH-hoa mdoule is mostly used by spatial audio professionals, recording engineers, content creators and researchers. Most functions in the BACCH-hoa module require the use of an HOA mic, such as the 32-capsule
Eigenmike (or the forthcoming 64-capsule version), which is quite expensive.
The 3dm (3D Mixer) module can indeed be used by audiophiles (who like surround sound) to emulate a multi-speaker surround sound system over a pair of speakers. The 3dm module requires discrete (i.e. decoded) multi-channels on separate buses (i.e. internal channels) that are then represented as virtual sound sources positioned in 3D space, using the 3dm module’s GUI, to be at the virtual locations of the corresponding speakers of a surround sound speaker configuration (e.g. Dolby 5.1, 7.1 and Atmos). The BACCH-3dm module then produces a binaural downmix (using either a generic pre-loaded HRTF, or the individual HRTF of the listener measured a priori in an anechoic chamber) and sends the resulting 2-channel signal to the output module of BACCH-dSP where it is filtered by a BACCH filter designed for the particular speakers used and sent out to the outboard stereo DAC to provide an emulation of multi-speaker surround system via only two speakers.
The Mac OS does not presently allow access to the Dolby-decoded N discrete channels so these must ne decoded by an outboard Dolby decoder (e.g. a receiver or an HDMI audio extractor) and sent to the Mac as N discrete PCM signals. We have recently built such a system for emulating 5.1 surround playback through two speakers at the request of a well-known audio critic who is finishing an extensive review of the
BACCH-SP (Theoretica’s standalone processor) for a leading audio magazine, to be published later this year. The system takes the HDMI signal from a 5.1 DVD or SACD (file or disc) player into a
Vanity Pro HDMI extractor that decodes the DSD audio signal (or Dolby coded surround from a DVD source) into 6 PCM signals, cleans the phase noise inherent in HDMI audio, thus greatly reducing the jitter, then sends the 6-channel PCM audio through AES/EBU to a
Lynx AES16e-SRC PCI Expresscard connected to a Mac mini running the BACCH-dSP application. There, the BACCH-3dm module, where the virtual sources are positioned by the GUI in 3D space following the standard prescription of the ITU 5.1 speaker configuration, produces a downmix of the 6-channel audio to a 2-channel binaural signal using one of the 10 pre-loaded HRTFs in the BACCH-dSP HRTF library (or the HRTF of the intended listener, if that measured HRTF is available). The binaural downmix is then processed by a BACCH filter in the output module of BACCH-dSP and the stereo signal is finally sent to the outboard DAC for playback through two speakers. (In the particular case of the audio critic reviewing the BACCH-SP the final processing through the BACCH filter was done on the BACCH-SP, connected via USB to the Mac mini, instead of the BACCH-dSP application on the Mac mini.)
To enhance the accuracy of the 5.1 surround speakers emulation, we measured the individual HRTF of the audio critic in the anechoic chamber of Princeton University’s 3D3A Laboratory, and used that HRTF on BACCH-3dm to produce the downmixed binaural signals.)
Since the BACCH-3dm mixer allows instantiating up to 20 virtual sources, a similar approach can be used to emulate an Atmos system if an Atmos decoder is available.
We plan to eventually offer such pre-configured 5.1 (and 7.1) emulation system (including the Vanity Pro HDMI extractor and the Lynx AES16e-SRC PCI Express) as an option for surround sound enthusisats who wish to emulate surround sound playback through the BACCH-SP processor or the BACCH-dSP application of BACCH4Mac Pro.
Regards,
Adam @ Theoretica