I have been trying to build a gnuradio AM broadcast receiver, but without success. I have tried a lot of combinations, but all of them produce a very distorted audio. I have an NBFM receiver using the same FunCube input and USB audio output which works very well, so they don't seem to be the problem. Below are two flowgraphs of my attempts. Any help will be appreciated.
OK, I have found the answer: the tuning is critical. Similar to tuning a SSB signal which shifts the voice frequencies, tuning an AM signal not only shifts the voice frequencies, but distorts the audio until you get right on the carrier frequency.
Another minor issue is audio overload. Turning down the volume eliminates that problem.
@Kevin Reid AG6YO I looked at the source code for the AM Demod block, and the Complex to Mag -> Add Const(-1) -> Low Pass Filter combination is what is inside the AM Demod block. I was just experimenting with making them separate.