Conversion to other Surround Sound formats
From Ambisonia
Contents |
[edit] Conversion to 5.1
[edit] Conversion to DTS-CD G-format
- This article by Richard Elen describes the conversion to DTS-WAV.
- Another description of how to do this can be found on Paul Hodges' site.
- Daniel Courville also has a howto here (which includes a discussion on converting higher order ambisonics to 5.1)
[edit] Conversion to Dolby Digital
With Mac OS X.
Once the B-Format stream is converted to 4.0, 5.0 or 5.1 (see references in the previous Conversion to DTS-CD G-format section), a Dolby Digital encoded G-Format DVD-Video can be easily authored with Compressor and DVD Studio Pro, both part of Apple Final Cut Studio.
The 48 kHz / 24 or 16 bit mono files (one per channel to be encoded) are fed to Compressor. Suggested settings are to adjust the dialogue normalization to -31 dB, Center and Surround channels downmix to -6 dB and to turn off the 90 degrees phase shift in the Surround channels. The bitrate should be set to the maximum allowed on DVD-Video, 448 kbps. In the case of a 5.0 mix with source files at 24/48, the size of the resulting AC3 file will be about twelve times smaller then the total source files.
This AC3 file is then imported in a DVD Studio Pro project. With a very basic menu and a still image as video track, the resulting DVD-Video can be burned directly from DVD Studio Pro or exported as a DMG file that can be distributed and later burned with software like Apple Disk Utility or Roxio Toast.
As an alternative, Roxio Toast has a DVD authoring mode called Music DVD (Audio Menu) that allows quick and dirty creation of a DVD-Video for audio-only playback. To avoid the multichannel AC3 files from being downmixed and re-encoded to Toast default two channel AC3, the files have to be dragged to the Toast window while pressing the Option (Alt) key. Toast will create a menu for the DVD and a still image for each track.
It should be noted that AC3 files are directly playable (like the DTS files on Ambisonia) with the VLC Media Player software. VLC is available for Windows, Mac OS X and Linux. One could then also include on a DVD-Video a non-multiplexed AC3 file, thus giving the end-user more playback options. Such a file, to be directly read by a software player, could use the maximum possible bitrate of 640 kbps allowed for a generic AC3 file and a 44.1 kHz sampling rate since it won't be tied in with a video stream.
[edit] Conversion to AAC
There is a highly-regarded free command line program for making AAC files, NeroAACEnc, available from the makers of the CD-burning software Nero. It requires either 2-channel or six-channel input, so a square decode (see the DTS pages for justification of this) needs to be packaged up with empty channels for the C and Lfe channels. Richard Dobson's interlx program does this very easily (it will insert a channel of silence without a file being required).
[edit] Conversion to DVD-A
If you are using Steinberg's WaveLab to manipulate ambisonic files, it is practical also to use it for burning DVD-As of G-format files (which sadly have to be generated outside WavLab). The sample rate and time are somewhat limited, as it doesn't include MLP.
[edit] Conversion to Vorbis
[edit] Conversion to FLAC
[edit] Conversion to WAV
Richard Dobson has written a suite of command line programs for packing and unpacking between single-channel and multi-channel WAV and WAV-Ex files. A few ambisonic manipulations are also included. Interlx is currently the only way to generate a fully correct B-format file following the .AMB specification.
[edit] Conversion to Binaural / 'Stereo'
- Aristotel Digenis has a C library that uses the MIT Kemar HRTFs here.
- Aristotel also has binaural conversion plugins for bidule
- Charles Gregory wrote Bformat2Binaural, which is a VST (for the PC) for conversion from B-format to binaural.
- TetraProc (Linux/OS X) is an A-Format to B-Format converter (see its main entry under Conversion and Calibration Software), but it can also output binaural and 'stereo'. Because it can accept B-format as input, it can be used as a (real time) B-format to two channel converter. (See the screenshot on the TetraProc website for the controls available for selecting the various possible outputs (Blumlein, XY, etc. with choice of angles as well as choice of azimuth and elevation).)
- Rapture3D output options include five HRTF sets, crosstalk cancelled stereo, Matrix QS, Matrix SQ, UHJ Stereo and compatibility modes for Dolby Stereo, Dolby Pro Logic and Dolby Pro Logic II.
