What does it mean? This Equalizer.

Quote:

I have computed for Einstein over july or august.
It was the computing associated with aricebo, i mean.
And I have seen, in the einsteingraph a kind of equalizer, like when we hear mod on Amiga.
I think at first it was music, but there was no sound.
So an equalizer without sound, somebody can tell me what it was.
Thank You very much.
Meskine Mohamed

I think it is a spectrum of frequencies which Arecibo is scanning. No sound.