built this TWIN -T - long time ago with the idea to be able to adjust the RISE and Fall TIME individual(via steering diodes) using the 3 variable resistor POTs for pitch, symmetry & rise/fall time circuit also uses a 5V regulator to stabilize the pitch and a 10K output resistor before going to audio input of recording laptop's LINE INPUT jack then into the screen recorder...the audio you hear is coming directly from this TWIN-T circuit(through an audio isolation transformer)
not shown on the PIC of the TWIN-T is the external LC parallel resonant circuit to get rid of most of the audio harmonics(at the trade off in elongating the rise & fall time)(depends on the "Q" of the coil & cap/circuit etc.. too much "Q" and sounds too mushy or 'ring-EEEE' )
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Here is a picture of the TWIN-T sine wave oscillator CW NOTE waveform at 60wpm\
another TWIN-T sinewave CPO keyed by FLdigi's serial port RTS pin feature... reducing HUM and background noise form the CPO using a simple gate...with adjustable rise/fall time
this demo uses ZAMGATE to provide the 'gating function' the sidetone is a keyed by fldigi and its serial port RTS PIN keying mode... TWIN -T sine wave oscillator with shaped edges...