Spectrum DSP M2 - DSP Configuration Value Adjustments; DSP Noise Reduction Parameters; DSP Automatic Notch Filter Parameters

Spectrum DSP M2 User Manual V1.1
Notes about adjustment of DSP-related configuration values:
DSP Noise Reduction parameters:
The DSP Noise Reduction is active in either the DSP NR or NR+NOT mode and it performs
noise reduction be detecting the coherent (e.g. non-random) properties of the human voice
and quickly adapting a filter to pass those frequencies and blocking the other frequencies.
The “strength” of this filter may be adjusted using the menu item #10, “DSP NR Strength” -
but be very careful with this as it easy to go overboard with this setting. If it is set too high,
the artifacts caused by the noise reduction (e.g. a “hollow” or “watery” sound) can be worse
than the interference than you are trying to remove!
The default setting is a good place to start, and carefully increase experimentally on signals of
varying quality to get a “feel” the effects.
It should be noted that “DSP NR BufLen” and “DSP NR FFT NumTaps” will also interact
with the efficacy of the “DSP NR Strength” setting, sometimes making a particular “strength”
setting weaker, sometimes making it “stronger.
Again: Remember that the “DEFLT” button will restore the settings to usable defaults!
DSP Automatic Notch Filter parameters:
The DSP Notch filter is an “Automatic” notch filter that will immediately “seek and destroy” any
CW (continuous) carrier that it finds, but it should have a minimal effect on the normal human
voice. It is active in the “NOTCH” and “NR+NOT” modes, but it is always disabled when in
the CW mode as it would make such operation impossible.
The notch filter operates within the signal path prior to the AGC and the DSP NR operation,
so a strong “tune up” signal will not cause the S-meter to deflect when the notch filter is
active, but note that the AGC is still active and the receiver may still de-sense if this signal is
very strong and cause the lower half of the S-meter to flash red.
Also note that the presence of a strong carrier may also cause some “intermodulation”
distortion – both from mixing products within the transceiver's analog circuitry, but also due to
the dynamic limitations of the A/D converter as well as artifacts in the mathematical
calculations being carried out in the SDR itself!
Note:
• The notch filter may be useful in AM mode to eliminate the “tweet” that appears when
tuned very close to the center frequency. If you are listening to a shortwave broadcast
station, note that the automatic notch may occasionally “attack” music with interesting
results!
Operation at very high NR “strength” settings (e.g. >= 35):
P 46