v1.280: spectrum peak hold, AM/NBFM de-emphasis
From the CHANGE_LOG file. Thanks to Sam, M1FJB, for the de-emphasis suggestion.
v1.280 April 8, 2019 Spectrum improvements: Add peak hold function. When running toggle "Peak" button to clear and restart. Last spectrum filter, filter parameter and peak hold setting saved in browser cookie. Audio improvements: Added de-emphasis control on audio tab. Standard 50us NA and 75us EU attenuation profiles. AM/NBFM modes only. Attenuation curves may not be 100% correct. Needs measurement. Should help reproduce flat passbands transmitted by AM/NBFM stations using pre-emphasis. Will also help with listening fatigue caused by excessive high-frequency gain. Fixed bug that caused distortion in 3 channel mode when audio bandwith at 20.25 kHz maximum.