Would it be possible to add a y-axis scale to the spectrogram in some future fb2k version? Spectrum's got one, VU meter's got one. It'd be really useful for judging what frequencies various encoders chop off. Without a scale it's pretty hard to guess (in both log and linear scales).
The Foobar spectrogram only shows info down to 50Hz, unfortunately, so not really sure how useful the scale would be. I hope it becomes full bandwidth one day.
With the bottom end cut off the spectrogram is more visually appealing in a player. At normal FFT sizes the bottom end is large ugly interpolated pixels, or the top turns into long streaks when FFT is increased. I hope the spectrogram can be made "multi-resolution" where the low end extension is analyzed with a bigger FFT and combined into the same picture (like in Izotope RX but with fewer "steps" for performance). But I have no clue how hard this is to do. If you do add a scale, make it barely visible (just a few dots or font color without much contrast against the background).