QED DAV FLX1 solid core oxygen free copper cable 75 Ohms SPDIF with 75 Ohm RCA plug, gold plated contacts.
Use to connect your CD player, streamer, or Blu-Ray player to DAC.
This is a bargain high-quality SPDIF RCA to RCA cable.
Background
Q: Why do digital cables make a difference – isn't digital "perfect sound forever"?
A: Because years ago, the designers of the digital audio interfaces decided that the audio signals should be sent imperfectly in real-time, rather than perfectly but late!
Our day-to-day experiences of sending digital signals are that they arrive perfectly, so what is different about audio? "I don't get errors when I save my Word document to my hard drive or send an email to my cousin in the US; how is it so hard to send a signal 1m between two hi-fi components?"
The critical difference between Hi-Fi and digital documents being sent is that the audio signals are sent IN REAL TIME WITH NO BUFFERING OR ERROR CORRECTION
In the case of a document sent across the word or to the printer, the data is transmitted in packets and assembled by the receiving machine; in the event of an error, there is time to ask for the signal to be re-sent it, is error corrected, so the result is 100% perfect. This all takes time.
The audio signal has no time for any of this. It is sent as a "continuous stream" (Hence the phrase "Streamer") in real-time, so there is no time to process it. If there are errors, then they affect the sound.
Why "In real-time"? - this was decided years ago in the audio industry to allow video and sound to be synchronised - otherwise, lip-sync issues will be caused when playing a DVD or watching TV.
The SPDIF interface is applied not only for CD players but also for DVD, Blu-Ray, Streamers etc., not just audio.
How do better cables help?
Jitter
The phrase "digital cables" is a misnomer. All cables are lengths of wire or glass fibre, through which ANALOGUE voltages or pulses of light are sent. In the case of a wire, the analogue signal is a so-called "square wave" representing the 1's and 0's of the digital signal. In theory, this should be perfect; however, in practice, this "square wave" is rarely square - instead, it has rounded edges.
The rounder they are, the more timing errors are introduced, called "jitter". (How does the receiving machine know where the transition from "1" to "0" is if the edge of the wave is not a sharp vertical transition but a curve or angled line?)
Reflections
In addition, as the signal hits the end of the cable, it is partially reflected, overlaying an out-of-phase rounded square wave on top of the original signal. This again contributes to errors. Longer cables reduce this issue; short cables are not a good idea.
Interference
Finally, Radio Frequency interference and Electromagnetic Interference can also introduce errors in the signal and affect the receiving equipment.
This emphasises the need for good shielding; in some cases, using Ferrite beads can help with some special equipment. (They can also hinder if incorrectly specified).
The better the cable, the squarer the wave, the less reflection, and the less spurious signals from interference.