Quick answer: Yes. LPCM passes over S/PDIF coax, but only two channels, and the practical ceiling is about 96 kHz at 24 bit, with 192 kHz working on some device pairs and not others. For 5.1 you need a compressed bitstream such as Dolby Digital or DTS, because the interface cannot carry six channels of uncompressed PCM.
LPCM over coaxial cable: rates, limits and setup
Your player is set to output uncompressed audio, the cable is a coax run into the receiver, and the receiver displays a stereo signal instead of the surround mode you expected. Nothing is broken. LPCM over coax has a channel count and a rate ceiling, and most sources quietly downmix rather than tell you why. The next few sections cover what actually travels on the line, where the ceiling comes from, which formats need compression instead, and how to set the source so a working cable is not the first thing you blame.
What LPCM looks like on a coaxial link
LPCM is uncompressed pulse code modulation: each sample is sent as a number, with no perceptual coding and no reconstruction step beyond the digital to analog conversion. On a coax link it rides inside S/PDIF frames, two channels interleaved, with the word clock recovered from the data stream. Because nothing is compressed, the required bit rate scales directly with sample rate, bit depth and channel count. That is the whole story behind the limits: stereo at 44.1 kHz needs roughly 1.4 Mbit per second before framing, and stereo at 96 kHz at 24 bit needs several times that. The interface was sized for two channels, and it stays inside that budget. That bit budget sets every limit that follows, and it explains why a cable cannot be blamed for a channel count the interface never carries.
The rate ceiling most people underestimate
The working ceiling on coax is about 96 kHz at 24 bit. Some device pairs will lock at 192 kHz, and some will not, which is why a blanket claim in either direction is wrong. The limit is not only the cable: the transmitter, the receiver chip and the clock recovery all contribute, and a long run at a high rate narrows the margin further. Optical uses the same frame structure with a similar ceiling, and plastic fiber can be slightly less forgiving over distance. If a source offers 192 kHz, test it on your actual hardware before planning a system around it. A receiver that mutes instead of distorting is telling you the truth about its own limit, and that mute is a feature rather than a fault.
Why 96/24 is the working limit
At 96 kHz and 24 bit, stereo LPCM already produces a bit rate close to what the consumer interface was designed to carry, including framing overhead. Doubling the sample rate doubles the payload, and the margin disappears. Interconnects, receivers and even the plug can absorb a small mismatch at 96 kHz and fail at 192, which makes 96 the number to design around.
What happens at 192 kHz
Two outcomes exist: the pair locks and plays, or the receiver mutes, clicks or drops to a lower rate. There is no partial success. If it locks, the run is short and both ends support it. If it does not, do not buy a longer or fancier cable hoping to fix it, because the limit sits in the interface and the chips, not in copper purity.
When compression is the only way to get 5.1
Six channels of uncompressed PCM do not fit through S/PDIF coax. The route to surround on this interface is a compressed bitstream, typically Dolby Digital or DTS, which carries five discrete channels plus a low frequency channel in a fraction of the space. The receiver or processor decodes it back to six channels. That is still a digital signal on the same 75 ohm cable, and the source has to be set to bitstream rather than PCM for it to work. If the source is set to LPCM and the disc is 5.1, most players downmix to stereo and send that, which is exactly the symptom in the opening paragraph. The bitstream is still digital S/PDIF on the same 75 ohm line; only the contents of the frame change.
Bitstream or PCM, one at a time
The player sends one or the other, never both. Set to PCM and a 5.1 disc arrives as stereo; set to bitstream and a stereo CD usually still plays, because most receivers decode PCM as well. Pick the setting that matches most of your material, and change it per disc only when that disc demands it and you are willing to walk back to the player menu.
Why the receiver display is the check
The display shows the incoming format, the sample rate and the channel count, which is the only reliable evidence of what the cable actually carried. A logo lit on the front panel is not a measurement. If the display reads stereo PCM, the source downmixed, and no amount of cable swapping will change that. Confirm the reading twice, once with the disc playing and once paused, since some players renegotiate the format at a stop.
Setting the source so the cable is not blamed
Open the audio output menu on the player, console or computer and look for two settings: the output format and the sample rate. Set the format to bitstream if you want surround from a 5.1 source, or to PCM if you want the downstream DAC to do the decoding. Set the sample rate to 96 kHz or lower unless you have tested 192 on that exact combination. On a computer, disable exclusive-mode sharing if the operating system keeps resampling. Then confirm on the receiver display that the incoming rate and channel count match your intent, not just that sound is present. Write both settings on a card in the setup menu if the remote makes them hard to reach, because a firmware update can quietly reset both to defaults.
Where the limit bites in practice
Three situations expose the ceiling. A media player with high resolution files at 192 kHz feeding a receiver that only accepts 96, where the player silently downsamples. A game console set to LPCM output into a coax-only soundbar, which yields stereo instead of surround. A disc player whose menu defaults to PCM, so every 5.1 disc arrives as two channels. In each case the cable is fine and the setting is the fault. The diagnostic habit worth building is to read the receiver display before touching hardware, because the displayed rate and channel count tell you what arrived. Everything else, including the cable, the plug and the shield, only protects the margin those settings established before any signal reached the wire.
Formats over S/PDIF coax
| Format | Over coax? | Max rate | Note |
|---|---|---|---|
| Stereo LPCM 16/44.1 | Yes, always | 44.1 kHz | Standard CD rate |
| Stereo LPCM 24/96 | Yes, always | 96 kHz | Common working ceiling |
| Stereo LPCM 24/192 | Device dependent | 192 kHz | Test before relying on it |
| Dolby Digital 5.1 | Yes, always | Compressed bitstream | Decoder unpacks six channels |
| DTS 5.1 | Yes, always | Compressed bitstream | Decoder required downstream |
| Multichannel LPCM 5.1 | No, needs HDMI | Not applicable | Interface is stereo only |
Real-World Application Scenarios
Three real cases. A home theater where a disc player feeds an AV receiver over coax and the surround mode only appears once the player is switched from PCM to bitstream. A desktop audio rig where a computer sends 24/96 LPCM to a DAC and anything above 96 clicks, so the operating system output is capped there. And an integration project where a signage player drives zone amplifiers over coax and the spec has to state 48 kHz stereo LPCM as the contract, because 5.1 was never going to travel on that line.
Related Guides on This Site
Start with the coaxial S/PDIF digital audio reference for framing and impedance. Readers comparing transport types will want the note on whether optical is the same as S/PDIF, and the wider comparison of S/PDIF versus optical covers distance and interference. For build details on the copper side, see the digital coax cable page.
Frequently Asked Questions (FAQ)
Q: Does coaxial cable support uncompressed audio?
A: Yes, for two channels. S/PDIF coax carries linear PCM with no compression, up to about 96 kHz at 24 bit in normal use. The restriction is channel count and rate, not the coding scheme. Uncompressed stereo is exactly what the interface was built to move.
Q: Can LPCM 5.1 pass through a coaxial cable?
A: No. The interface carries two channels of linear PCM, so six channels of uncompressed audio do not fit. Surround over coax uses a compressed bitstream such as Dolby Digital or DTS, which a decoder expands to 5.1. For uncompressed multichannel you need HDMI or a multichannel analog path.
Q: What is the maximum sample rate for LPCM over coax?
A: About 96 kHz at 24 bit is the practical ceiling. Some device pairs accept 192 kHz, but that is device dependent rather than guaranteed, and long runs make it less likely. Design for 96 kHz and treat 192 as a bonus you verify on the actual hardware.
Q: Why does my receiver show stereo when the disc is 5.1?
A: The source is almost certainly set to PCM output, so it downmixes to two channels before sending. Change the player audio setting to bitstream, then check that the receiver display shows the surround format. A coax cable cannot create channels that were never sent.
Q: Does a better coax cable raise the LPCM rate limit?
A: No. The limit comes from the interface definition and the transmitter and receiver chips. A cable that meets 75 ohm with good shielding protects the margin you already have, which can matter on a long run at 96 kHz. It cannot add capability the standard does not define.