Quick answer: An HDMI to TOSLINK extractor takes the audio stream out of an HDMI signal and sends it down an optical cable, while passing the video to the display. It must read the display EDID, decide which audio formats the sink will accept, and strip the audio before the video leaves. Optical output is limited to two channel PCM or compressed 5.1, and the two are not interchangeable.
These boxes are popular with monitors that have no speakers, projectors with no audio path, and older AV receivers that predate HDMI. Each case has a different audio format requirement, which is where most installations go wrong.
What the extractor removes
HDMI carries video, audio and control in one stream. The extractor splits the audio packets away from the video and re-clocks both. The display still receives a valid HDMI signal, but the audio portion is either removed or replaced with silence, depending on the mode.
Pass-through or strip
In pass-through mode the display still gets audio, which is useful when the TV speakers should keep working. In strip mode the audio is removed so the display does not complain about unsupported formats. Choose strip if the TV shows an audio format error.
EDID handling
The extractor presents an EDID to the source that describes both the display and the extractor’s own audio ability. If that EDID claims 5.1 support while the optical output is set to PCM, the source sends a format the box cannot carry, and you get silence instead of downmix.
Handshake order matters
Power the extractor before the source, then the display. The box reads the display EDID at power-up, and a source that boots first may latch a format the extractor has not yet learned. If the picture works but the audio is wrong, unplug the HDMI at the source for ten seconds and reconnect.
PCM against compressed 5.1
TOSLINK carries about 125 Mbps of optical data, enough for two channels of uncompressed PCM at 192 kHz or a compressed Dolby or DTS bitstream at 48 kHz. It cannot carry six channels of uncompressed PCM, because that exceeds the standard. This is the single most common source of confusion.
Stereo sources
Set the source to PCM and the extractor to PCM. Dialogue, music and games all work, and the receiver does the digital to analog conversion.
Surround sources
Set the source to bitstream and the extractor to pass-through. The receiver must decode Dolby Digital or DTS itself. If the receiver only handles PCM, set the extractor to downmix, which folds the surround mix into two channels.
Extractor, ARC and eARC compared
| Method | Direction | Formats | Cable | Best for |
|---|
| Extractor | HDMI in, optical out | PCM 2.0, Dolby 5.1 | HDMI plus TOSLINK | Monitor or projector audio |
| ARC | TV to receiver | PCM, Dolby 5.1 | HDMI with ARC | Single cable to soundbar |
| eARC | TV to receiver | Up to Dolby Atmos | HDMI 2.1 certified | Object audio |
| Optical direct | Source to receiver | PCM 2.0, Dolby 5.1 | TOSLINK | Legacy receiver |
| Analog extractor | HDMI in, RCA out | Stereo only | HDMI plus RCA | Powered speakers |
Practical scenarios
- Monitor with no speakers: extractor in strip mode, optical into a desktop DAC, source set to PCM, video passed to the monitor at its native resolution.
- Projector with a legacy AV receiver: extractor set to bitstream, optical into the receiver, receiver set to auto detect, and the projector fed by the extractor’s HDMI output.
- Console on a computer monitor: the extractor must pass 4K 60 Hz for the video and downmix to stereo for the monitor’s headphone jack.
- Conference room with a ceiling speaker system: extractor on the room PC output, optical to the amplifier, and a fixed EDID so the PC never negotiates a format the amplifier rejects.
FAQ
Why is the optical output silent?
The source is sending a format the extractor cannot pass, usually multichannel PCM. Set the source to PCM stereo or to Dolby bitstream, and make sure the extractor switch matches.
Does the extractor reduce video quality?
No, if it is rated for the resolution and refresh rate in use. A 4K 30 Hz extractor will cap a 4K 60 Hz source, which looks like a video fault rather than an audio one.
Can I get 7.1 surround through TOSLINK?
No. The optical standard carries at most a compressed 5.1 bitstream or two channel PCM. For 7.1 or object audio you need eARC over HDMI.
Next step
Decide whether the receiver decodes surround or only stereo, then set both ends to the same format and lock the EDID. The HDMI eARC cable guide covers the newer single cable route, the TOSLINK cable page covers connector types and lengths, and the optical audio cable guide explains bend radius and loss.
