Bitstream vs PCM – HDfury Vertex glossary
Bitstream sends the sound still packed, PCM sends it already unpacked. Where the decoding happens, and what it means for Atmos.
Sound on a disc or stream is packed up to save space. Someone has to unpack (decode) it before speakers can play it.
Bitstream means the player sends the sound still packed, and the receiver unpacks it. PCM means the player unpacks it first and sends it ready to play. It is like getting a packed suitcase versus getting the clothes already on hangers.
Does the HDfury Vertex pass bitstream audio and PCM?
YESYes. Over HDMI the Vertex passes bitstream (Dolby and DTS, including TrueHD and Atmos) and PCM unchanged; it does not decode. The optical output carries only stereo or 5.1 Dolby/DTS, so multichannel PCM does not fit there.
How to use it with the Vertex:
- Check the incoming audio in the USB GUI lines AUD0/AUD1 (p.27).
- RS232: #get audiochbot or #get audiochtop returns LPCM or bitstream for that input (p.48).
- See the details in DV/IF > CAPTURED AUDIO INFOFRAME (p.36).
- Give the player an EDID with full audio, such as an 'All Sound' table, so it may send bitstream (p.15).
What it is
PCM (pulse-code modulation, often written LPCM) is plain, uncompressed digital audio: the actual sound samples. Bitstream means the coded format itself, such as Dolby Digital, DTS, Dolby TrueHD or DTS-HD Master Audio, is sent unchanged over HDMI or optical, and the receiver decodes it.
For lossless formats, both routes can give the same sound quality, as long as the decoding is done correctly. The differences are practical. With bitstream the receiver shows the real format and can use its own processing. Dolby notes that Atmos plays through players connected to an AVR via HDMI 'with the bitstream output function engaged'. When a player decodes to PCM, the height and object information of Atmos or DTS:X is usually lost, and you get a normal channel mix.
PCM over HDMI can carry up to 8 channels. Over optical S/PDIF, PCM is limited to 2 channels, so surround sound over optical has to be bitstream (Dolby Digital or DTS).
On the Vertex
The Vertex passes both bitstream and PCM over HDMI without changing them (p.104). The manual lists PCM up to 192 kHz and compressed audio (IEC 61937), including Dolby TrueHD, DTS-HD MA, DD+, DTS:X and Atmos (p.111).
You can check what arrives. The USB GUI shows the detected input audio type (p.25), the DV/IF tab shows the captured audio InfoFrame (for PCM usually sample rate and speaker count, for bitstream often only default values) (p.36), and RS232 '#get audiochbot' / '#get audiochtop' returns LPCM or bitstream for the selected input (p.48).
On the optical output the Vertex gives stereo or 5.1 Dolby/DTS; the analog jack is stereo only (p.104-105). Multichannel PCM does not fit through optical.
Common questions
Which sounds better, bitstream or PCM?
For lossless tracks they can sound the same if decoding is correct. Choose bitstream if you want Atmos or DTS:X with height effects, or if you want the receiver to show the real format.
Does the Vertex decode Dolby or DTS to PCM?
No. It passes audio over HDMI unchanged and does not downconvert it (p.104).
How can I see if my player sends bitstream or PCM?
Look at the audio type in the USB GUI or use RS232 '#get audiochbot' or '#get audiochtop' (p.25, p.48).
- https://professional.dolby.com/en-in/tv/home/dolby-atmos-for-the-home/
- https://en.wikipedia.org/wiki/S/PDIF
- manual p.36
- manual p.48
- manual p.104
- manual p.111