Spectrum DSP M2 User Manual page 42

The above offsets the display as follows:
DSP related items:
DSP NR BufLen – This is the length of the De-Correlation delay buffer. In order for the
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DSP to tell a voice signal from noise, it must have a sample of each, but given the
absence of a separate noise source, we have to "simulate" one by delaying the original
signal to "de-correlate" it. If we delay it too little, it will resemble the voice too much
and be ineffective. If we increase the delay, we can improve the performance but if we
delay too much we end up with an "echo" type effect and a sluggish response.
This value must always be larger than "DSP NR FFT NumTaps", below. If
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this rule is violated, the number will turn RED and DSP NR operation will
become ineffective.
DSP NR FFT NumTaps – This is the number of taps in the FIR (filter) comprising the
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DSP noise reduction filter. A smaller number of taps implies a more agile filter, but also
one that is less accurate while a larger number of taps is more precise and potentially
slower to respond: A more "precise" filter may also reduce the actual performance in
that the automatic calculation of the filter's parameters – which are, by their nature,
imprecise, may "miss the mark". A higher number will increase processor loading
and slow the user-interface response.
This value must always be lower than "DSP NR BufLen", above. If this
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rule is violated, the number will turn RED and DSP NR operation will
become ineffective.
DSP NR Post-AGC – This determines whether the DSP noise reduction will take place
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before the audio filtering and AGC or after the audio filtering and AGC. The net effect
will be the same, but there will be important differences as perceived by the user:
"NO": DSP Noise reduction takes place before filtering/AGC – The
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operation of the DSP noise reduction will affect the S-meter reading. Because
the noise reduction occurs prior to the AGC, the "quieting" caused by the noise
reduction will be compensated by the AGC and the perceived "quieting" effect
caused by the noise reduction will be reduced. Note that this can give the
impression that the noise reduction is less effective than it actually is!
"YES": DSP Noise reduction takes place after filtering/AGC – This
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operation of the DSP noise reduction does not affect the S-meter reading. If
very "heavy" noise reduction is occurring, this can cause the perceived audio
level to drop, requiring that one "rides" the volume control, particularly if there
are weaker signals, buried in the noise, amongst strong – a situation that can
exaggerate the volume differences! Be careful if you are wearing
headphones when using this setting!
Comment: It is recommended that one make judicious use of the "RF Gain" control
(RFG) to reduce the receiver gain when using the DSP – particularly if "DSP NR Post-
AGC" is set to "NO" - to reduce the amount of noise that is heard under "no signal"
conditions.
DSP Notch ConvRate – This adjusts the convergence factor ("mu") of the filter and will
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have an effect on how quickly it "attacks" a CW note. Because of the nature of the
filter, this parameter's effects aren't as obvious as those of the "Strength" adjustment of
the noise reduction filter. The higher the number, the more quickly it will "attack" and
notch a tone that appears in the passband. It should be noted that very high numbers
Spectrum DSP M2 User Manual V1.1
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