Hi
I made some digital interconect cables from special, very flexible, 75 Ohm video cables and compared them with regular high quality interconnect cables on my scope, the selfmade digital cables show faster edge rise time time on the digital trace, 7 nS instead of 21 nS, did anyone else measure that? Must try and do some listening tests....
Cheers, Tom.
I made some digital interconect cables from special, very flexible, 75 Ohm video cables and compared them with regular high quality interconnect cables on my scope, the selfmade digital cables show faster edge rise time time on the digital trace, 7 nS instead of 21 nS, did anyone else measure that? Must try and do some listening tests....
Cheers, Tom.
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Digital cables are made to support RF. Because they are optimized for that, they may be less well optimized for carrying analog audio information. For one example, quad star type audio cable, sometimes even for unbalanced connections, may tend to sound better than cables of other construction due to its superior rejection of stray magnetic coupling in the environment.
Audio band signals (20Hz - 20kHz) are considered narrowband in frequency, and so, the bandwidth related performance of a cable carrying them is of relatively small concern - although, high-capacitance cable, or long runs (translating in to a high total capacitance) of cable can present a problem. Digital audio signals (meaning, S/PDIF here), on the other hand, are considered relatively wideband, at a few Megahertz in bandwidth. At such frequencies, A.C. factors, such as an impedance matched transmission path, become quite important. As a result, the physical construction of a cable (including it's connectors) intended for optimal digital audio signal transmission are different than for a cable meant only for analog audio band signal transmission.
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Digital versus analog
Hi
Will try both as soon as I got some time to do it, will inform you.
Cheers, Tom.
Hi
Will try both as soon as I got some time to do it, will inform you.
Cheers, Tom.
For analogue audio, an advantage of 75 ohm coax compared to cheap PVC-insulated cable is the much lower capacitance: about 67 pF/m for 75 ohm coax cable with solid polyethylene dielectric while the typical PVC-insulated cinch cables can have 280 pF/m or even higher.
Just because it's measurable doesn't mean it's audible because audio measuring devices are much more sensitive than human ears. Yes, listening test would be helpful as long as it's objective listening test.
If cable capacitance for audio is concern: Guitar Cable Capacitance Chart • Comparison of pF Ratings by SHOOTOUT! Guitar Cables UK
Cables can make a difference in digital signal transfer. I've seen and heard it in digital video and audio with SPDIF, AES, TOSLINK, DVI, HMDI and SDI (but not DP). Some people will tell you that digital either works, or it doesn't. That's not entirely true. In digital video you'll see signal problems as sparkles in the picture before obvious glitches and failure. In digital audio it's harder to identify.
However, with short cable runs, most SPDIF signals do just fine even on crap cable because the receiver chip fixes things enough that it doesn't matter. With video SDI and HD-SDI the receiver chip works hard to EQ the signal back into a usable form after long cable runs. It's part of the protocol.
Since you have a scope, you might have a look at the eye pattern of the signal with your different cables. That can tell you a lot.
However, with short cable runs, most SPDIF signals do just fine even on crap cable because the receiver chip fixes things enough that it doesn't matter. With video SDI and HD-SDI the receiver chip works hard to EQ the signal back into a usable form after long cable runs. It's part of the protocol.
Since you have a scope, you might have a look at the eye pattern of the signal with your different cables. That can tell you a lot.
Digital sources are usually 75 ohms, and digital inputs are also likely that, too. Use a cable with a 75 ohm characteristic impedance, like RG59-U or similar. Using a different cable impedance can cause reflections that could increase BER (Bit Error Rate) due to reflections in the cable.