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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: RE: I Shouldn't Comment, But......... posted by theaudiohobby on May 19, 2009 at 05:36:44:
"An AM radio is a RF receiver that's is almost unique in it susceptibility to RFI(EMI actually), static exists because AM receivers attempt to demodulate spurious signals to an audio frequency. Amplifiers for example are not receivers and consequently much less susceptible."
Stress the word "less". Which doesn't mean totally immune.
"> > The RFI is from the transistors in the DSP chips switching on and off with the data stream, sampled at a constant rate. Each bit in essence resembles a square wave, whose bandwidth goes well into the RF range. (Given the same power dissipation per bit, a 24/96 signal puts out over three times as much RFI relative to a 16/44 signal via NOS playback.)
"The are a quite holes in this text. But rather than dwell on those,"
You *think* there are holes, but if you make such claim, you should be able to explain why...... Otherwise it's a claim no different from those about Brilliant Pebbles or wooden knobs.......
"it is sufficient to say that this whole section falls apart because it ignores the key reasons why an AM radio is particularly susceptible to EMI."
I choose a medium that's "susceptible" because it **reveals** a problem. One can put a wood block next to a digital source, hear nothing, and then claim there is no RFI problem......
"And sources of interference can be anything from a transformers, power supplies to oscillator circuits, claiming that AM radio static noise is as a result of DSP chips is a bit of a stretch."
Oscillator circuits...... Why would someone design an audio component with oscillator circuits??
"Which brings me back to my original point, you first have reliably identify the interference source."
I first knew about the AM interference thing with a demonstration. The DAC was run with the active DSP chips in place. There was mucho interference on the AM radio. The DAC was powered down, the chips were removed entirely, and then the DAC powered back on (just the power and analog circuitry running). The interference on the radio went away, just about entirely. (I recall a faint "60 Hz" buzz on the radio, relative to when the DAC was powered down.) The DSP chips were then plugged back into the sockets, the unit powered on, and the interference returned. (This was part of a seminar at a now-defunct audio store in Los Angeles. It took place in the mid-1980s. I remember those Sheffield "Stop Digital Madness" T-Shirts being sold during the seminar.)
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Follow Ups
- RE: I Shouldn't Comment, But......... - Todd Krieger 05/19/0911:31:32 05/19/09 (0)
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