In January and October of 1992 I wrote two QEX articles on a project that another Ham and I worked on called the "Hamblaster". We developed a DSP based sound card that used filter programs for noise reduction and auto notch.
A feature that we added proved to be quite interesting in some respects and corrected problems where the DSP was outside the AGC loop. First of all the Hamblaster had its own AGC loop that maintained an optimal baseband level. There was an on screen option to freeze filters. My theory was "Why design an auto notch that continuously adapts". You only need to converge on the interfering carrier once. After that, there's no need to re-adapt. If the interfering carrier changes, to readapt, you can press the auto notch button again. Because everything was done in software, we added buttons on the PC screen where you can set a parameter to automatically freeze the auto notch after a given time or you can manually freeze it. This worked well and after the notch was locked to carrier, there was no distortion. We even added a freeze button on the noise reduction. I noticed that when the filter adapted to ones voice. The LMS algorithm was, for the most part, was optimized to the person's voice characteristics and the filter was optimal for the whole QSO. The drawback was that it took several tries to get it right. Some times the filter lock on the high frequency elements of speech and other times on the low frequency components but it reduced noise to a certain degree without the usual artifacts in the noise floor. I thought that this would be an interesting feature to add to the K3 in the next firmware upgrade. Jack WA9FVP Willco Electronics. ----- Jack WA9FVP Sent from my TRS-80 :-) -- View this message in context: http://elecraft.365791.n2.nabble.com/Auto-Notch-Filter-Freeze-tp7564753.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
