Analog-Digital?
LAC -- Fri, 05/18/2007 - 15:29
Feel kinda silly asking this, but here goes anyways...
Am I correct to assume that when you connect an analog component, (like a turntable) to a pre-amp (for instance), that the source dictates what kind of cable to use --analog source = analog interconnect, digital source (cd player) = digital cable etc. How can you tell one cable type from the other- digital, analog, speaker, AV? What would be the effect of using an analog cable with a digital source? I suspect that with AV cables you should have a video conductor, but what about the signal coming from a digital amp, or for that matter, a tube amp being fed to the speaker? And if you are using a single ended speaker cable (not bi-wired), is there any difference in cable construction? They're all presumebly conveying the same signals- ..or are they? I kinda find it somewhat confusing, not knowing my audio ABC.s..
lac
Sorry that no one else has responded. I just returned from vacation.
There are many different types of cables used in audio systems. The typical low-level signal cable, that goes between sources, preamps, and into power amps, is a co-axial design with RCA connectors. There is a single center wire attached to the pins of the RCA connector plugs, and another wire and/or a shield attached to the outer gripping parts of the plugs.
These come in analog and digital varieties. The digital cables are made to have a certain impedance to radio-frequency signals, while the impedances of the analog variety may vary widely. The digital cables are made to carry digital signals (pulses representing ones and zeroes) only, such as from a transport to a DAC. The output of a CD player is analog, as the DAC is inside.
The impedance is not the resistance. The resistance may be very small (fraction of an ohm), but the impedance is what a radio-frequency signal "sees" when it enters the cable (typically 50 or 75 ohms) due to the cable geometry. Digital pulses require good radio-frequency response by the cable to be timed accurately.
If the cable impedance does not match the sending and load impedances, some of the energy is reflected at the ends. This causes problems for digital gear, as the reflections are mixed up with the following pulses. This is why your equipment specifies the impedance of the digital cables you should use with it. The equipment might work with an analog cable, but probably not as well as it would with the proper digital cable.
There are other types of signal cables for analog use. Some are shielded to reduce the noise that gets into the cable. Phono cables are typically shielded, but many of the cables for use from CD players and the like may not be shielded. Some designers feel the shielding causes problems with the analog signal.
Speaker cables are specialized for high current and have spade or pin connectors on each conductor. Most speaker cables are not shielded.
All cables and power cords have the ability to interact with radio-frequency noise present on the AC, in the air, and coming from audio equipment circuits. We cannot hear this noise directly, but it mixes with the audio signal inside the equipment and causes spurious audio tones that mimic natural overtones. Some cables are designed to reduce this interaction.
Hi Al,
Thank you for respnding to my querry. Your explanation is clear and informative. This throws some light on the ongoing debate about short interconnect-long speaker cable and vice-versa. It also helps me understand why some power cables act like filters etc. Very much appreciated.
LAC
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