The mixer runs above unity for any ordinary input - the Hilbert kernel's L1 gain
is 2.51, so amplitude 0.7 peaks at about 1.76 - and the output was hard clipped
to fit. Clipping squares the waveform off and generates odd harmonics, which the
widened waterfall would now put on screen.
Measured, the harmonics happen to be harmless today: TARGET_HZ is a quarter of
the sample rate, so 3f, 5f, 7f and 9f all fold back onto the tone itself and
out-of-band energy stayed at 0.00%. That is a coincidence between two constants,
not a property of the design. At a 700 Hz target the third harmonic folds to
1100 Hz - inside the analysis window, where no filter may remove it and the model
would read it as a second tone.
So two changes, because neither alone is enough. A peak-following gain scales the
mixer output to fit rather than clipping it: measured 0 of 3200 samples on the
rail, against a clipped waveform parking there for much of every cycle. And a
95-tap windowed-sinc band-pass over the model's window removes whatever the mix
leaves outside it - images, harmonics, the far sideband - measured at 58-60 dB
rejection with 0.09 dB of passband ripple and out-of-band energy down to 0.0002%.
The gain is shared across chunks so it cannot step at a boundary, and the filter
carries tap history for the same reason the Hilbert filter already did.
The band-pass adds 47 samples of linear-phase group delay, 14.7 ms, which delays
the keying envelope without distorting it - 4% of a dot at 40 WPM.
CwToneShifterStreamingTest's boundary criterion was wrong, and the band-pass
exposed it: distanceToBoundary measured only forward, so the first samples of a
chunk came out 320 away from "the" boundary and counted as interior when they are
the far side of the same seam. Both filters need samples ahead of the output they
are producing - 32 for the Hilbert transform, 47 for the band-pass - and with the
distance measured to the nearest boundary either way, interior divergence is
0.000116 against a 0.01 budget.
Also: the CW transcript now follows the newest text, but only while the operator
is already at the bottom, so scrolling back to read earlier traffic is not undone
by the next decoded character.
mckero
0889a3bd88