Can I use any RCA cable for S/PDIF digital audio?

Yes, but only for short runs under 1.5 meters and at CD quality (44.1 kHz). For 96 kHz or longer cables, you need true 75-ohm coax. Generic analog RCA cables often cause jitter, clicks, or dropouts due to impedance mismatch.

Why does impedance matter for digital audio cables?

S/PDIF requires 75-ohm impedance. Mismatched cables cause signal reflections that blur data edges, creating timing errors (jitter). Above 5–10 ns jitter, the receiver can lose lock and produce no sound or static bursts.

Is a 'digital coaxial cable' different from a regular RCA cable?

Yes, it's built to 75-ohm spec. But you don't need to pay premium prices—any 75-ohm video cable (yellow RCA composite cable) works identically and is often free or under $5.

How long can an S/PDIF cable be?

True 75-ohm coax handles 10–15 meters reliably. Generic RCA is limited to 1.5–3 meters for CD quality, and often fails entirely beyond 5 meters regardless of sample rate.

What are the signs my cable isn't working for digital audio?

Intermittent clicks, pops, audio dropouts, or no sound at all. Problems often appear when switching to higher sample rates (96/192 kHz) or after extended use when the receiver heats up.

What Is HDMI 2.1 QMS (Quick Media Switching)

Can RCA Cables Carry Digital Audio (SPDIF)?

1. The Short Answer: Yes, But With Caveats

Yes, a standard RCA cable can carry an S/PDIF digital audio signal.
In fact, most consumer gear uses exactly that – an RCA-terminated 75-ohm coax cable.
But not every RCA cable works well.
The difference comes down to impedance, shielding, and length.

2. What Is S/PDIF Over Coax?

S/PDIF (Sony/Philips Digital Interface) has two physical forms: optical (Toslink) and coaxial.
The coaxial version uses a single RCA connector.
The signal is not analog audio. It’s a bi-phase mark code (BMC) at a fixed bit rate.
For CD-quality audio (44.1 kHz, 16-bit), the raw data rate hits 2.8224 Mbps.
For 96 kHz / 24-bit, that jumps to 6.144 Mbps.
Dolby Digital (640 kbps) or DTS (1.5 Mbps) fits easily, but the clock is still embedded.

So yes – the plug is RCA, and the wire is coax.
But the specification calls for 75-ohm characteristic impedance.

3. Impedance Mismatch: The Real Problem

A standard analog RCA cable (red/white) is typically uncontrolled impedance – often 50–150 ohms, but not consistent.
Most fall into the 50–70 ohm range.
Some cheap cables drop to 40 ohms at certain frequencies.

Here’s the issue:
At 2.8 Mbps, the signal’s third harmonic reaches ~8.5 MHz.
At 6 Mbps, harmonics go past 18 MHz.
Impedance mismatch causes reflections.
Reflections blur the data edges.
That raises the jitter (timing error).
Jitter above 5–10 ns can cause clicks, dropouts, or no lock at all.

Cable Type	Impedance (typical)	Max reliable S/PDIF length
True 75-ohm coax (video/digital)	75 Ω ±3%	10–15 m
Standard analog RCA	50–70 Ω (uneven)	1.5–3 m
Very cheap thin RCA	<50 Ω	<1 m (unreliable)

3.1 Real-world test data

In a 2017 test by Audio Science Review, a 2m generic RCA cable dropped S/PDIF lock at 96 kHz sample rate.
The same length of Belden 1694A (true 75Ω) worked fine at 192 kHz.
At 44.1 kHz, both worked – but the generic cable added ~2.1 ns of RMS jitter vs 0.7 ns on the proper cable.
Not audible for most, but borderline for sensitive DACs.

4. Why Do People Say “RCA Cables Don’t Work for Digital”?

Because they tried a long, cheap analog cable.
At 5 meters, many analog RCA cables fail completely.
The signal eye diagram closes.
The receiver chip (e.g., CS8416 or AK4118) loses PLL lock.
Result: no sound, or random static bursts.

Manufacturers don’t help.
They sell “digital coaxial cables” that look identical but cost 3x more.
In truth, any good 75-ohm video cable (e.g., RG-59, RG-6) with RCA ends works perfectly.
Monoprice’s 1.5m digital coax cable sells for $4.
A premium analog RCA interconnect might cost $50 – and perform worse for digital.

5. When Does It Actually Work Fine?

Short runs – under 1.5 meters.
Low sample rates – 44.1 or 48 kHz.
Decent analog cable – not the flimsy thin type that comes with a DVD player.

Example:
A 0.9m RCA cable from a 1990s VCR (unknown impedance) passed 44.1 kHz S/PDIF without errors in one informal test.
At 96 kHz, same cable failed after 20 minutes (heat build-up in the receiver’s PLL).
So “works” depends on your tolerance for random dropouts.

6. Technical Limits at a Glance

S/PDIF voltage: 0.5V to 0.6V peak-to-peak into 75Ω.
Max cable loss (per spec): ~6 dB at 6 MHz.
75Ω coax loss (RG-59): ~4 dB/10m at 10 MHz.
Analog RCA loss (typical): higher and uneven – often 6–10 dB/10m at 10 MHz.

Uneven loss across frequency distorts the signal shape.
That adds jitter.
Too much jitter (above ~20 ns peak) = wrong bits.

7. Summary: Use the Right Tool, But Don’t Overthink It

Use case	Works?
1m decent RCA, 44.1 kHz	Yes, reliably for most gear
2m generic RCA, 96 kHz	Maybe – test it
5m cheap RCA, any rate	No – buy real 75Ω coax
10m true 75Ω coax, 192 kHz	Yes (with good receiver)

Bottom line:
An RCA cable can carry S/PDIF digital audio, especially for short runs at CD quality.
But don’t push it.
If you hear clicks, stutters, or silence, swap in a proper 75-ohm coaxial digital cable.
Better yet – use an old composite video cable (yellow RCA). That’s already 75Ω.
Free, and technically correct.

FAQ: Frequently Asked Questions About RCA Cables and S/PDIF

1. Can I just use any old red-and-white RCA audio cable I have lying around for digital audio?

Answer: Possibly, but only under ideal conditions. A standard analog RCA cable can physically connect the devices and may work without issues for very short runs (under 1.5 meters) and low sample rates (like standard CD quality at 44.1 kHz). However, because analog RCA cables don’t guarantee the required 75-ohm impedance, they are unreliable for longer runs or high-resolution audio. You might experience random clicks, dropouts, or a complete failure to get a signal lock.

2. Why does impedance matter for a digital signal? Isn’t it just sending 1s and 0s?

Answer: It’s a common misconception. At high speeds (like the 2.8 to 6+ Mbps of S/PDIF), the cable acts as a transmission line. If the cable’s impedance doesn’t match the source and receiver’s 75-ohm specification, part of the signal reflects back. These reflections blur the sharp edges of the digital waveform, creating timing errors (jitter). If the jitter gets too high, the receiver chip can’t correctly interpret the 1s and 0s, leading to data errors and audio dropouts.

3. I see “digital coaxial cables” for sale that look just like RCA cables. Are they a scam?

Answer: They aren’t a scam, but they are often overpriced for what they are. A properly manufactured “digital coaxial cable” is guaranteed to meet the 75-ohm impedance specification and have good shielding. The article points out that you don’t need to pay a premium for a branded audio cable. A standard, high-quality 75-ohm video cable (like the yellow-tipped composite video cable that came with older game consoles or DVD players) is technically identical and often works perfectly for S/PDIF.

4. I’m using a 6-foot (2-meter) analog RCA cable for my DAC, and it seems to work fine. Should I replace it?

Answer: If you aren’t experiencing any issues (clicks, pops, or the audio cutting out), you might not need to rush out and buy a new cable. However, as noted in the article’s test data, your generic cable might be introducing higher jitter (around 2.1 ns) compared to a proper cable (0.7 ns). While this is rarely audible, it can push sensitive DACs to their limit. If you ever upgrade to higher-resolution audio (96 kHz or 192 kHz) or move your equipment further apart, you will likely start experiencing problems, and a proper 75-ohm cable will be necessary.

5. My receiver doesn’t have an optical (Toslink) input, only a coaxial RCA input. How can I connect my TV?

Answer: You need a coaxial S/PDIF cable. As the article suggests, your best and most cost-effective option is to use a standard composite video cable (the one with the yellow RCA connector). Since video signals also require 75-ohm impedance, this cable is technically correct for the job. Just plug one end into the “Digital Audio Out (Coaxial)” on your TV and the other into the matching input on your receiver.

6. What are the first signs that my RCA cable isn’t up to the task for S/PDIF?

Answer: The most common signs are intermittent issues rather than a complete failure. You may hear:

Brief clicks or pops in the audio.

Audio dropouts where the sound cuts out for a split second.

The receiver failing to lock onto the signal, resulting in no sound at all, especially when switching between sample rates (e.g., from a 44.1 kHz song to a 96 kHz movie soundtrack).

7. Is it okay to use a 75-ohm coaxial cable for analog audio, too?

Answer: Absolutely. You can use a 75-ohm cable for any analog audio or video signal. The cable is physically compatible. The only minor “downside” is that it is often stiffer and less flexible than a typical analog RCA cable due to its construction, but it will carry the analog signal perfectly well. It just isn’t a two-way street—analog cables often fail for digital, but digital cables always work for analog.