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jkeny 25th January 2011 01:13 AM

RF & Audio
 
I'm prompted to start this thread by something that has been rattling around in my brain for a while (yes, before anybody else says it, there's a lot of empty space in there to allow rattling :)) & I don't have the experience or knowledge to answer it myself. Maybe some of the more experienced could pitch in.

It was recently prompted by this post from DF96 on the Bybee thread "..... Stopping RF from getting into audio components can improve the sound, yet nothing will show up in a purely audio test."

I wonder how many agree with this? Can it be explained & what is the underlying mechanism?

abraxalito 25th January 2011 01:20 AM

Its been my hobby horse for quite some time - many years in fact since reading an article in a hifi magazine back in the 1980s - probably it was HiFi Answers or HiFi world. The writer concluded that RF effects on electronics was a significant part of the puzzle regarding perceived audio quality.

In my own tinkering, I find that grounding is a huge part of making a piece of electronics sound good. I have a theory that grounding affects susceptibility to RF, but its early days yet and I have very little hard data. I've been trying to capture poor audio quality by recording the output of poorly grounded kit - so far, nothing has shown up.

sandyK 25th January 2011 01:25 AM

Quote:

Originally Posted by jkeny (Post 2445182)
I'm prompted to start this thread by something that has been rattling around in my brain for a while (yes, before anybody else says it, there's a lot of empty space in there to allow rattling :)) & I don't have the experience or knowledge to answer it myself. Maybe some of the more experienced could pitch in.

It was recently prompted by this post from DF96 on the Bybee thread "..... Stopping RF from getting into audio components can improve the sound, yet nothing will show up in a purely audio test."

I wonder how many agree with this? Can it be explained & what is the underlying mechanism?

John
It may not be readily measurable at the analogue output, but I expect that when using a suitable preamp with a wide bandwidth CRO, it would show up at the bridge rectifiers, and in the case of ingress into the NFB network via long loudspeaker cables as well.e.g. "frame buzz" from nearby TV transmitters.
Alex

abraxalito 25th January 2011 01:31 AM

I've had this link open as a tab in my browser for months as its such a good article outlining not just the technical aspects but also mentions some audible effects of changing grounding. Its been put up before, no harm to share it again :

SoundStage! Pete's Place - JPS Labs Superconductor Interconnects: A Technical Discussion (09/1998)

'RF and cables' is the heading about halfway down. I hope this doesn't encourage the thread to degenerate into another cables slanging match though :eek:

jkeny 25th January 2011 01:34 AM

Thanks guys,
Yes, let's not have this thread hijacked, please. I think this is a fundamental concept & needs an open, non-judgemental discussion.

There are those that claim if it can be heard then it should be measurable on the analogue output. I can understand this logic but wonder what is the logical trap in this thinking? I'm grappling with these contradictory viewpoints!

SY 25th January 2011 01:42 AM

The effects of RF, when audible, are easily measurable on the output in the audio band. For example, think of an extreme case- rectification and detection- where you can actually hear radio signals breaking through.

abraxalito 25th January 2011 01:46 AM

Quote:

Originally Posted by jkeny (Post 2445197)
There are those that claim if it can be heard then it should be measurable on the analogue output.

Well I do and don't subscribe to that view. I do in that something must be measurable, but I don't in thinking that that measurable thing must necessarily be audible - i.e. in the audible band. Its a fallacy to measure the output of say a CD player and say because there's no difference in the audio band therefore there can be no difference by the time its reached our ears.

The reason for this fallacy is overlooking downstream non-linearities. Intermodulation isn't zero in most amps/pres, especially when that's intermodulation with out-of-band signals.

abraxalito 25th January 2011 01:51 AM

Quote:

Originally Posted by SY (Post 2445202)
For example, think of an extreme case- rectification and detection- where you can actually hear radio signals breaking through.

Yes, I get this and would like to figure out how to get rid of it. Do I have to adopt valves? :p I agree, that's totally measurable. But how about lower level effects when we're not so sure that its the GSM phone making the difference? Do you discount those effects?

SY 25th January 2011 02:26 AM

Your example is somewhat inapt- the effect is still measurable in the audio band, just a bit further downstream of where it occurs. Agreed that two inaudible signals can intermodulate and produce something audible, but that produced signal is absolutely measurable in the audio band.

abraxalito 25th January 2011 02:44 AM

Quote:

Originally Posted by SY (Post 2445237)
Your example

Which?


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