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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: Hearing under noise floor: a test to hear posted by Jacques on June 18, 2006 at 13:07:15:
"Practically, the most powerful signal extractor I know are used on deep space board. Depending on the coding and the bit-rate, you can extract signals <-120dB under the noise floor. A very sensitive receiving principle used in this application involves an amp whose gain is switched between +1 and -1. You switch it at exactly the emitter's sent carrier. Over a long enough integration time, only signals very near of this frequency add and are not cancelled out. The longer integration time, the better S/N you get. But the lesser the telemetry bit rate can be."I'm not familiar with radiotelemetry from deep space probes however, I'd expect that an array of receivers spaced at different locations around the earth would receive simultaneously and integrate their signals after time compensation. By filtering at the known transmission frequency and owing to the fact that the noise is random while the desired signal is not, it should be possible to extract enough of the signal even at very low levels to gate a switching transistor. Further software enhancement taking into account the known nature of the noise could further enhance the extracted signal improving resolution. You can see this when NASA shows fuzzy photos without and then with enhancement using suitable algorithms. Using an array of antennas exploiting the geometric aspects of the physical nature of the rf fields is analogous to the fact that sound fields are also vectors, this is effectively also a vectored field at a known frequency. I'm not sure this has any application to high fidelity sound reproduction. Quite the opposite, the usable dynamic range would have to have a signal sufficiently "above" the noise floor to make it readily distinguishable from the background noise. An audio signal at or near the background noise level would be undesirable. Therefore the usable dynamic range would be the difference between the signal level at 0db and saturation minus the minimum acceptable S/N ratio. Am I missing something here. BTW, thanks for the downloads. For some reason, I wasn't able to run them. No idea why yet.
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Follow Ups
- Re: Hearing under noise floor: a test to hear - Soundmind 14:38:15 06/18/06 (0)
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