Quick Answer / Summary: Set the source to bitstream before blaming the extractor. TOSLINK and coaxial S/PDIF carry two-channel PCM or a compressed Dolby Digital or DTS stream up to 5.1, never six-channel PCM. The extractor must present a 5.1 capable EDID to the source; if it copies the display stereo EDID, the source downmixes. Check the source audio menu, then the EDID switch, then the decoder input, then the cable. Work from the source outward.
An audio extractor sits between a source and a display and must do two jobs at once: hand the source an EDID that promises 5.1 audio, and pass the video stream through untouched. Nearly every failure traced to these boxes is a negotiation failure rather than a dead TOSLINK port. The source is sending stereo PCM, or the extractor is copying the television two-channel EDID.
What the Extractor Has to Negotiate
The source reads the sink EDID over the DDC line before sending a frame. That block lists supported audio formats: two-channel PCM only, or PCM plus Dolby Digital and DTS. An extractor with a fixed EDID tells the source it accepts 5.1; a passive splitter repeats whatever the display reports.
Why the box must declare 5.1
If the extractor copies the television EDID, and most televisions report stereo PCM plus Dolby Digital, the source is entitled to send stereo. Players then downmix internally and the decoder receives two channels. Most units carry an EDID switch for exactly this reason, as these HDMI ARC audio extractor buying notes describe.
Bitstream versus PCM at the source
The console, set-top box or player also has an audio output menu. PCM forces the player to decode and downmix; bitstream passes Dolby Digital untouched. This is the most common cause of a stereo-only result from a working extractor.
Video Has to Pass Through Unchanged
The video path should be a wire. In practice the extractor holds a buffer and, on cheaper models, a scaler, so 4K60 at 18 Gbps can arrive as 1080p or 4K30. Anything that touches the stream also risks an HDCP handshake error, which shows as a black screen rather than a warning.
Checking bandwidth at the display
Ask the display what it receives. If it reports 4K60 before the extractor and 1080p60 after, the box is scaling. A unit rated for 18 Gbps should pass 4K60 8 bit 4:4:4; only a 48 Gbps unit passes 4K120.
HDCP and the split
An extractor that presents itself as a repeater must complete the handshake with both source and display. Splitting to a capture device often breaks it. If the picture goes black while audio continues, suspect HDCP before the cable.
TOSLINK or Coaxial: Same Data, Different Cable
Both outputs carry S/PDIF, so the format limits are identical and only the transport differs. The table compares them with the two HDMI audio return paths that people confuse with them.
The six-channel PCM trap
S/PDIF cannot carry six channels of PCM. A source set to multi-channel PCM is downmixed to stereo, and no setting on the extractor recovers it. Select Dolby Digital or DTS in the source menu, then read the format name on the decoder display.
Cable and connector rules
TOSLINK uses a 1 mm plastic fiber with a square connector and should not bend tighter than about 25 mm. Coaxial S/PDIF is a 75 ohm line on an RCA plug, so a proper S/PDIF RCA cable works where a thin audio patch lead may not. Keep both runs under 10 m.
| Output | Channels | Bitrate | Cable | Carries |
|---|
| TOSLINK | 2 PCM or 5.1 | 1.5 Mbps | 1 mm plastic fiber | DD, DTS, PCM |
| Coaxial RCA | 2 PCM or 5.1 | 1.5 Mbps | 75 ohm coax | DD, DTS, PCM |
| HDMI ARC | Up to 6 | About 1 Mbps | HDMI cable | DD, DD+, PCM |
| HDMI eARC | Up to 8 | Up to 37 Mbps | HDMI 2.1 cable | DD+, TrueHD |
| Analog RCA x6 | 6 | Not applicable | 6 shielded leads | PCM only |
The Four-Stage Test
Test in order and change one thing at a time. First the source menu: bitstream, Dolby Digital, not PCM. Second the EDID switch on the extractor: 5.1, not copy. Third the decoder: correct input, and read the format display rather than the volume. Fourth the link: swap the S/PDIF lead for a known good one.
If the decoder shows PCM stereo at stage three, the fault is upstream and the cable is irrelevant. If it shows no signal at all, the port or the lead is at fault. That split resolves most returns without a bench test, as these coaxial digital inputs show.
Two Installations, Two Faults
Console, television and an older receiver
A receiver with only coaxial and TOSLINK inputs received stereo from a console. The console audio menu was set to PCM, and the extractor EDID switch sat on copy. Moving the switch to 5.1 and the console to bitstream produced Dolby Digital at 640 kbps.
Projector room using ARC
A projector fed an extractor from its ARC port, and dialogue arrived 120 ms late. The television was decoding and re-encoding. Taking audio from the source instead of ARC, with the display muted, cured the delay.
Frequently Asked Questions
Why does my extractor only output stereo?
The source is set to PCM or the extractor is copying the display EDID. Set the player to bitstream and the EDID switch to 5.1, then check the decoder format display.
Does TOSLINK support 5.1 surround?
It supports a compressed 5.1 bitstream such as Dolby Digital or DTS, not six channels of PCM. Optical and coaxial S/PDIF share that limit, which is a format rule, not a cable fault.
Will the extractor reduce 4K video quality?
A passive unit rated for 18 Gbps should not. If the display reports a lower mode after the extractor, the box is scaling or the cable is marginal. Compare the input info page with and without it.
Can I use one extractor for two displays?
Rarely. Splitting the HDMI output usually breaks the HDCP handshake with at least one sink, and the extractor reports the lowest common EDID. Use a matrix with proper HDCP handling instead.
Do I need an extractor if my TV has ARC?
Only if the audio system lacks HDMI or the ARC port is already in use. ARC carries Dolby Digital, so an extractor adds a stage rather than capability unless you need TOSLINK or coaxial.
Related resources: HDMI ARC audio extractor buying; S/PDIF RCA cable; coaxial digital inputs
