tech

I reworked the spectrum analyzer around lock-free, wait-free queues so the device read thread never blocks long enough to corrupt its own buffer. More work per graph, yet CPU dropped from 120% of a core to 65%. Then -O3 made the data vanish entirely.

My first idea for the waterfall display was drawing millions of 1x1 rectangles per second. That didn't work at all. Treating it as a raw RGBA image and letting Core Graphics render it directly was so much faster. Now I just need an HF satellite overhead.

Current, average and max are finally drawing on the right scale, and those nine evenly spaced spikes turn out to be broadcast radio stations. 2,048 measurements per block, ~190,000 per second, windowed, transformed and smoothed into a pretty graph. Now for the waterfall.

I told someone I was building a spectrum analyzer. "A spectral man-a-lizer??" came the reply. Confusion aside, my filter chain is working and I can correctly claim to have seen radio station WPBS, even if I have never heard it.