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RE: Just to confirm - in your experience, the changes (drivers, players etc.) on computer side....

Posted by Tony Lauck (A) on September 5, 2014 at 07:16:42

In Reply to: RE: Just to confirm - in your experience, the changes (drivers, players etc.) on computer side.... posted by Jaundiced Ear on September 4, 2014 at 19:29:58:

"'Unfortunately, the computer creates a huge amount of noise.'

How much is "huge" and how has it been measured?"


Huge, as in my wife complained about my computer(s). She picked up the interference on her AM radio. Her radio was running on batteries, so the noise didn't have benefit of any wires at all, no SPDIF, USB, power cords, etc... If you look on the back of computerized devices you will see little stickers with FCC numbers, CE numbers, etc... These are all certifications that these devices emit an "acceptable" level of interference, where acceptable is a political compromise between powerful players, in this case TV broadcasters and FM broadcasters vs. computer manufacturers. AM radio wasn't so politically connected at the time these regulations came into effect a few decades ago. Because of the technical characteristics of audio, there were no standards associated with audio. It has always been the case that audio equipment has been able to defend itself against interference, and it is the responsibility of audio equipment manufacturers to do so. (Following a long line of cheapness, they seldom did.) In the 1950's as a teenage radio ham my transmitter caused interference with nearby record players and I helped solve the resulting problems as a good neighbor, not because I was legally required to do so.

The same situation applies where the interference comes over power wiring and there are filters that can be applied. (Also described in the 1957 edition of the Radio Amateur's Handbook.) The situation also applies to signal wiring (SPDIF or USB). Here the equipment to measure this is available, but it is very expensive and a major investment for boutique manufacturers.

If you pick up an AM radio and set it near your computer (or CD player) you will get an idea of what is going on. You will hear different patterns of noise when the computer is idle and when it is active, e.g. playing music. You will hear these patterns change when using different players or adjusting buffer sizes. All of this interference affects the analog equipment in a DAC and downstream amplifiers to some extent or other, depending on how much rejection the audio equipment has for spurious signals.

"If they had a standard "bad" transport that was very noisy while still bit perfect"

A cheap computer system might do just fine. :-) But a better way of testing would be to take a fairly good transport and pass the output signal through a purpose built box that deliberately adds various amounts, types, and frequency ranges of interfering noise. There are specs for how noisy an input signal is allowed to be and still be a "legal" signal that an SPDIF or USB receiver must accept as "bit perfect". This means there is a limit on how bad the noise can be on the signal wires, otherwise the system won't work without clicks, pops or dropouts. This limit puts a ceiling on how much noise the filtering circuit must be able to reject. The amount of rejection depends on the audio quality level desired. There are serious cost issues here, because the amount of rejection is limited by the number of isolation stages, power supplies, ground isolation, physical shielding, etc...

There are also differences of opinion as to how much residual noise is actually audible. These differences arise for various reasons, but the most controversial reason is probably that some listeners are willfully deaf while some other listeners willfully imagine non-existent differences. Hopefully, there will be few of either camp that will reply to this post. :-)


Tony Lauck

"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar

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