- Confused about the differences between SPDIF and optical?
- Wondering about the different use cases for each, and when to use one over the other?
- We address all your commonly asked questions in this complete guide
- Also, check out our guide to the differences between SPDIF and ADAT
Considering that SPDIF and optical are digital connections, some people might think they’re interchangeable or that SPDIF is a type of optical connection.
The truth is that SPDIF is a connection protocol that can sometimes use optical connections.
The first optical connection format, Toslink optical, was developed before SPDIF. As the audio industry has evolved, the use cases for each connection type have changed a bit, and depending on your workflow, you might find that one works better for you than the other.
SPDIF vs. Optical: A Quick History
SPDIF stands for Sony/Philips Digital Interconnect Format and was developed in 1980 by Sony and Philips for home theatre.
Optical, or TosLink optical, was manufactured by Toshiba in 1983 to connect CD players to receivers.
SPDIF vs Optical: The Differences
It’s important to note that SPDIF is simply the connection protocol rather than the cable or physical connection itself, whereas optical also refers to the cable or physical connection type.
- SPDIF uses electricity to transfer two digital high-fidelity uncompressed PCM audio channels or compressed 5.1 surround sound.
- Optical/TosLink utilizes fiber optic connections to transfer up to 8 channels of audio and is the standard protocol for ADAT audio transfers.
| SPDIF | Optical | |
|---|---|---|
| Signal quality | Relatively noise-free but still susceptible to noise | Clear, consistent signal |
| Interference | Due to the physical properties of electromagnetic current, some interference is possible | Free from interference due to the physical properties of light pulse technology |
| Use Cases | Stereo audio in/out for DVD players, TVs, speakers and some pro audio | Often used for transmitting Dolby decoders to sound equipment, consoles, and AV receivers |
| Limitations | Only handles digital signals, and cannot support lossless surround formats | Limited to 5.1 and stereo channels, cannot support lossless surround formats like DTS-HD or Dolby TrueHD |
| Overview | Useful for musicians working with digital signals prioritizing low-latency audio | A great solution for general home theater and hi-fi usage, and those who will benefit from wide-range compatibility and better energy consumption |
SPDIF vs Optical: When To Use Each
There are various reasons that you’ll want to use SPDIF rather than optical, and vice versa. Depending on your needs, one connection type might be better.
For music producers — it’s worth noting that your pro audio interface might offer you both connections. Some outboard preamps allow you to use the digital SPDIF out with an optical cable, while you can still get extra inputs via SPDIF in.
The main advantage of transferring audio via SPDIF is not just the capability for extra channels but also that you won’t need to convert your digital audio to an analog signal before transferring it to another device. Therefore, you’re less likely to lose quality in your audio signal. This makes them very attractive for pro audio use, and why you’ll see them in audio interfaces.
Optical is found commonly in home theater setups for their wide-range compatibility and better energy consumption. Nearly all audio devices and components will offer you optical connectivity.
Data Transfer Method and Connecting Multiple Audio Interfaces
SPDIF is generally better suited for connecting multiple audio interfaces because SPDIF will carry the clock source with the audio signal, meaning you won’t need multiple instances of DACs (Digital Analog Converters) to keep everything in sync.
This is called “digital clocking.” When you transfer digital audio from one device to another, it’s transmitted in a series of samples.
The more samples per second, the higher quality of the audio. To ensure the samples are being transmitted accurately, the device receiving the audio needs to know when each new sample will be played.
This is done using a “word clock,” a clock signal embedded in the SPDIF protocol.
It’s essential to use quality cables when you connect two devices via SPDIF. A subpar cable or shaky connection could result in a phenomenon known as “interface jitter” which can be heard as clicks and pops in the audio recording.
Cable Type
Depending on whether you’re using a SPDIF or optical connection in a recording studio versus a live setting, the cable type might be more important to you.
If you’re in a live setting, you’ll want a more durable cable that’s less expensive to replace if something happens during the show. In this case, there are a few things to keep in mind.
Even though copper wire is more vulnerable to interference, fiber-optic cables are more sensitive to physical damage.
Depending on the length of cable you need, it’s worth considering one over the other. If it’s a short run, you won’t have to weigh one risk factor against the other. If you need a longer cable length, you’ll need to be careful where you run it, especially in a live setting.
Number Of Audio Channels Transferred
If you need more than two channels of audio, SPDIF is your best bet, as it will give you up to 8 channels of audio. However, if you’re in a live setting, an optical cable might do the job instead since you’ll only need two tracks (which together make a left and right stereo mix).
One of the most versatile use cases for SPDIF is if you upgrade your audio interface and still want to use the old one for additional inputs and outputs. In this case, connecting the two via SPDIF would give you those eight extra audio channels.