Coaxial digital audio cables are commonly used to connect audio components like CD players and surround sound systems.
As a sound engineer, I’ve used coaxial digital audio during recording and editing audio. I also use it in my home theater for CD and Blu-ray audio. However, it’s not your only choice.
This article explores how coaxial digital audio works, including its advantages and limitations, and how to use it with different connection types.
Key Points
- Coaxial digital audio connections are commonly used to send audio from DVD/Blu-ray players, CD players, computers, and TVs to amplifiers, receivers, and soundbars.
- The digital audio format transmitted over coaxial cables is S/PDIF, like optical digital audio. This supports uncompressed PCM audio and compressed surround sound like Dolby Digital.
- Digital coaxial can be converted to and from digital optical or stereo analog audio connections using adapters.
Main Topics
Get Up To Speed on Coaxial Digital Audio
Coaxial digital audio is exactly what it sounds like – digital audio signals transmitted over coaxial cables. It sends uncompressed digital audio data between devices like Blu-ray players, AV receivers, TVs, etc.
You’re probably familiar with the typical RCA connectors for composite video cables. Well, coaxial digital audio cables use those same RCA plugs. Except, instead of video, they carry high-quality digital stereo audio.
S/PDIF (Sony/Philips Digital Interface Format) is the specific digital audio format used over coax. This allows the transfer of uncompressed PCM audio and compressed surround sound like Dolby Digital and DTS 5.1.
S/PDIF is the same digital audio format used by an optical connection.
The difference is that optical digital audio uses light pulses for transmission, and coaxial sends the audio data as electrical signals.
Optical connections are more common in modern AV devices like TVs and soundbars. In contrast, you may find a coaxial connection in older TVs and hi-fi components like CD and Blu-ray players.
Here is a selection of popular coaxial cables:
- Size: 3/6/10 feet
- 24K gold-plated connectors
- Color-coded connectors
- Size: 4 feet
- Gold-plated, split-tip RCA connectors
- Easy-grip and color-coded for easy use
- Size: 3/6/10/15/20/25 feet
- 75 ohm impedance
- Reliable build-quality
What Coaxial Connectors and Cables Look Like
A coaxial digital connection on your device looks like this:
A coaxial digital connection uses a single RCA connector, usually orange or black. Unlike stereo analog audio, which requires two cables for stereo, coaxial only needs one to transmit digital signals.
Devices like DVD players will have either a coaxial digital input or output, depending on whether they are designed to receive or send audio signals.
For example, a DVD player typically has a digital audio output to send sound to an AV receiver.
The coaxial port may be labeled as “coaxial,” “digital out,” “coax out,” or “digital in.” Make sure to check the labeling to identify the port correctly.
The RCA cable can plug into the port in either orientation, but it should fit snugly. You may need to push firmly to get a tight connection.
Coaxial digital audio cables for transferring audio look like this:
A digital coaxial cable has an RCA male connector at each end. For proper signal transfer, it should have an impedance of 75 ohms.
Yet, in the real world, many AV cables may not be 75 ohms – whatever it may say on the packaging.
You don’t need expensive “high-end” cables, as a decent-quality coaxial cable does not have to be costly. Something like this will be fine:
- Well-made cable with good shielding
- Available lengths: 3, 6 and 10 feet
- 75-ohm impedance for reliable signal transfer
- Color-coded
- Limited cable lengths
The key is using a well-made 75-ohm impedance-matched cable, which is not necessarily the most expensive.
Pay closer attention to construction quality for longer cable runs over 20 feet. However, an affordable yet sturdy cable will accurately transmit the digital audio signal for standard lengths.
You can also use a digital coaxial cable to connect AV receivers to subwoofers.
How Is a Coaxial Cable Wired?
Internally, a coaxial cable has four main components:
- A center core – usually made from copper wire.
- A dielectric (electrically insulating) plastic insulator.
- A braided metallic mesh (a shield for electromagnetic interference).
- An outer plastic coating protects the inside of the cable.
The coaxial cable’s noise-rejecting design makes it versatile for transmitting analog/digital signals, video, data, RF, and high-frequency waves.
Beyond digital audio, coaxial cable is commonly used for:
- Analog video, like composite RCA cables, where it shields against interference.
- Cable TV signals from providers to homes, enabling long-distance transmission.
- Ethernet data networking over existing coax (MoCA).
- Carrying radio waves up to a few GHz for antennas and instruments.
- Ham/CB radio uses it to connect transceivers to antennas.
Audio Formats Supported by Coaxial Digital
A coaxial digital audio connection supports uncompressed 2-channel PCM audio, Dolby Digital, and DTS surround sound up to 5.1 channels. It can also handle 6.1 channel formats like Dolby Digital EX and DTS-ES.
However, a coaxial digital connection does not support multichannel LPCM, Dolby Digital Plus, Dolby Atmos, DTS:X or high-definition audio such as DTS-HD Master Audio and Dolby TrueHD.
Due to licensing restrictions, you cannot play DVD-Audio or SACD audio.
7.1 soundtracks are only available in high-resolution formats, so they won’t play as intended. Your player’s manual will tell you how to handle any unsupported audio sent via the coaxial output.
The most common solution is to downmix the audio to stereo PCM – or the player may output a lower-resolution version.
Use HDMI cables to play any unsupported audio as intended. But for basic stereo and 5.1 surround, a coaxial digital audio cable will suffice.
When to Use Coaxial Digital Audio
The preferred method for transferring digital audio signals is via an HDMI connector. HDMI supports all audio formats and keeps video and audio together on one cable.
However, if HDMI is not an option, a coaxial digital audio cable is an excellent alternative for sending stereo or 5.1 surround sound between devices.
A coax out connects DVD players, computers, or CD players to AV receivers and amplifiers. Many TVs also have a coaxial audio output to connect to an external sound system, although optical outputs are more common nowadays.
If your devices have both coaxial and optical outputs, coaxial is typically preferable. The cables are more common and durable than optical cables.
But both cable types transmit identical digital audio data, so there is no audible difference.
If your devices use different connection types, you can use a converter to switch between coaxial and optical. The main benefit of using either over analog connections is maintaining pristine digital audio quality.
Do You Have to Use a Coaxial Cable?
It is recommended to use a 75-ohm coaxial cable to transmit digital transmissions because this will help avoid errors in the signal.
However, nothing stops you from using any RCA cable you have lying around – like a composite video cable. It should give you a working signal.
However, it’s best only to use one of these if you have no choice, so a proper 75-ohm digital cable is recommended.
How to Extend the Cable
What can you do if your digital coaxial audio cable is too short?
For example, you may be relocating your equipment, and the cable you were using needs to be longer.
Can you extend a digital audio coaxial cable? Yes, it’s easy.
All you need is to buy a female-to-female RCA adapter, which is also known as a coupler:
- Works with RCA video and audio cables
- Two pack for extending dual RCA cables - either two mono/video or one stereo.
- Gold-plated
- You might have issues if you create a very long cable.
Of course, you will also need another coaxial cable to connect to the other side of the coupler. So, if you already have a second coaxial cable, that’s great.
Then, connect the two cables with a single coupler, and you will be good to go.
Will this degrade the audio performance?
It shouldn’t do. The manufacturer says the couplers pictured above suit a digital audio RCA cable, so you shouldn’t get any glitching.
If you buy a different brand, check if they are suitable for digital audio RCA cables before you buy.
In an ideal world, it would be best to use a single cable that is the correct length – but adapters like these can be a cheap and easy solution if you need to extend a cable run.
Can You Convert Digital Coaxial to Optical Audio?
You’re in luck; you can convert digital coaxial to optical audio.
If you need to connect a coaxial output to an optical input, you can buy a coaxial-to-optical converter, which converts one S/PDIF type into another.
The one pictured below takes a coaxial digital audio output – like from your Blu-ray player – and converts it to an optical signal you can connect to your amplifier.
- Use it if you don't have the correct digital audio connections on your device
- Bi-directional so you can convert both ways
- Supports uncompressed stereo PCM audio and 5.1 Dolby Digital and DTS
- Works up to 30 meters
- Power connection required
Be careful when buying one of these. Some converters will only work one way – from coaxial to optical, for example. So it’s essential to buy the correct one for the job.
If unsure, you could play it safe and get a converter that can handle optical and coaxial S/PDIF audio.
The one suggested above is bi-directional, meaning you can convert digital audio signals either way – from coaxial to optical or from optical to coaxial.
However, a converter that only works in one direction might be slightly cheaper.
The model suggested above also sends the signal from both outputs at the same time.
Therefore, it can be used as an S/PDIF audio converter and as a splitter to simultaneously send the audio signal to two different places.
In some circumstances, that can be really useful.
Connecting a Digital Audio Out to an Amplifier
Many amplifiers and AV receivers have coaxial RCA digital audio inputs. These receive the digital audio output from the source device, like a TV or DVD player.
How do you connect the digital audio output to an RCA input on an amplifier?
Well, that depends on the type of digital audio output on your TV, DVD, or Blu-ray player.
As explained previously, there are two main types of digital audio output – coaxial and optical – so here is how you would connect them both.
Connecting a Digital Audio RCA Output to an RCA Input
Connecting to your amplifier’s RCA input is easy if your output device has a coaxial RCA audio connection.
You need to buy a 75-ohm RCA coaxial digital audio cable like the one below:
- Well made and from a popular brand
- Dual shielding to reduce interference
- Available lengths: 2, 4, 8, 15 and 25 feet
- Gold-plated connectors
Then, connect this from the RCA output on your TV or DVD player to the RCA input on your amplifier. Job done.
Just make sure that you buy the correct length of cable for your system.
Give yourself a bit of slack for re-routing the cable in the future – or if you move your equipment – but try and get roughly the right length for the job in hand.
So, try to avoid buying a 10m cable for a 2m distance, for example.
Learn more: Home theater wiring tips and advice
Connecting an Optical Digital Audio Output to an RCA Input
If your digital audio output is optical, it’s a little more tricky – but not much.
Ideally, you connect the optical output to an optical audio input on your amplifier.
However, what if your amplifier only has a coaxial RCA input? In that case, you must convert the connection from optical to coaxial.
You can do this with an optical to coaxial RCA converter like the one below:
- Bi-directional: coaxial to optical or optical to coaxial
- Audio support up to 24bit/192kHz
- Switch to select the correct source
- Requires power
In this case, connect an optical cable from your output device to the converter’s optical input.
Then, connect the converter’s RCA output to the amplifier’s RCA input with a coaxial digital audio cable.
It’s a bit more complicated but easy enough when you have the correct converter.
How to Split the Signal
What if you wanted to send a single coaxial digital audio output to two different playback devices?
For example, send a TV’s audio output to a soundbar and a separate DAC – or from a CD player to an amplifier and a DAC.
The solution is quite simple. You can buy an RCA Y-adapter audio cable similar to the one below:
- Suitable for digital audio or subwoofer connections.
- Short cable adapter for easy installation
- Pro-grade connectors and build quality
- You'll need to buy extra RCA cables for each connection.
All you need to do is connect the single male RCA to your coaxial audio output. You then have two female RCA connections to send audio into the inputs of your two devices.
The two inputs on your devices may also be female connectors, so you will need an extra male-to-male RCA digital coaxial cable to complete each connection.
Like the one above, a Y-cable can connect two subwoofers to an AV receiver with a single subwoofer output.
Converting Coaxial Digital to Analog Audio
So, here’s the thing. You have a digital coaxial output on your Blu-ray player. However, you only have stereo RCA inputs on your amplifier.
How will you hear the audio from your movie on your speakers?
Like the model pictured below, the solution is to buy a coaxial digital audio-to-analog RCA converter.
- Optical and coaxial digital audio inputs
- Accepts PCM and Dolby/DTS 5.1 input audio
- 192/24 lossless decoding
- Output volume control
- Only outputs stereo analog audio, not surround sound.
This device will accept a coaxial or optical digital audio signal and output it as stereo analog audio.
This converter can be used anytime you need to convert S/PDIF digital audio to analog stereo audio – and it even has an internal volume control.
If you want to send movie audio to a stereo speaker system, a converter like this can make this a simple process.
An advantage of this device is it accepts more audio formats than most converters. You can send stereo PCM audio from your TV or disc player – or it even decodes 5.1 Dolby Digital and DTS.
Many converters will only accept a digital PCM audio signal. While this is OK for some devices, many digital audio outputs only support Dolby Digital or DTS audio.
Of course, if you only need PCM audio, you can get a cheaper converter that doesn’t have built-in decoding.
Stereo Analog to Coaxial Digital Conversion
There may be a time when you want to send analog audio into a digital audio input.
For example, you might have an old tape deck with stereo analog outs that you want to connect to your speaker system or soundbar with only coaxial digital audio inputs.
In this case, you must buy an analog RCA to digital coaxial audio converter.
- Supports uncompressed 2-channel PCM/LPCM stereo audio
- Converts to S/PDIF coaxial or TOSLINK optical audio
- Sampling rate: 48 kHz
- Not bi-directional - analog to digital only.
With the converter pictured above, you would connect the stereo analog audio output from your tape deck to the RCA inputs.
Then, connect a digital audio coaxial cable from the output to your amplifier or soundbar. This device also has the advantage of supporting an optical audio output.
Frequently Asked Questions
Here are some quick answers to popular questions about coaxial digital audio:
What Is a Digital Audio Coaxial Cable?
A coaxial cable for digital audio transfers S/PDIF stereo and multichannel audio between devices. It has a male RCA connector at each end, a coaxial build and a 75-ohm impedance rating for the cable and connector.
What Is the Coaxial Output on a TV?
The coaxial output on a TV is for sending digital audio. You would use it to connect the sound from your TV to a speaker system or soundbar.
What’s the Maximum Length of a Digital Audio Coaxial Cable?
While there is no specified limit, a well-built cable should transmit digital audio up to 50 feet (15 meters) – and maybe more. However, much will depend on the construction of the cable and the electronics in the source and destination devices. As with most audio cables, it’s best to keep the length to a minimum.
What’s the Difference Between a Coaxial and Optical Digital Audio Connection?
Coaxial and optical digital audio connections transmit identical S/PDIF signals and support the same audio formats. The main difference is the connector and cable type. Optical uses thin fiber optic cables, while coaxial uses more robust 75-ohm coaxial cables better suited for longer distances. But both deliver uncompressed stereo PCM audio and compressed 5.1 surround sound.
Can You Use an RCA Cable for Coaxial Audio?
Coaxial digital audio cables are RCA cables. However, not all RCA cables are suitable for digital audio. Cheap RCA cables may work over short distances, but for best results, use a dedicated 75-ohm coaxial digital audio cable. While standard RCA cables can transmit the signal, a proper coaxial cable will ensure signal integrity, especially over longer runs.
About The Author
Paul started the Home Cinema Guide to help less-experienced users get the most out of today's audio-visual technology. He has been a sound, lighting and audio-visual engineer for around 20 years. At home, he has spent more time than is probably healthy installing, configuring, testing, de-rigging, fixing, tweaking, re-installing again (and sometimes using) various pieces of hi-fi and home cinema equipment. You can find out more here.
