I've been using a USRP software-defined radio to try to send an amplitude modulated signal to a very basic receiver, basically just a piece of wire as an antenna, over a very short distance. The signal, a wav file of me counting to ten, is transmitted clearly enough to be understood by a human, but not by a speech-to-text program. The received signal is also clearly much higher in frequency than the transmitted signal. I took FFTs(illustrations provided below) of the sent and received signals and it seems clear to me that the lower frequencies in the signal are not being transmitted as strongly. The solution I've been trying to work on is adjusting the signal I'm transmitting by amplifying the lower frequencies of the signal and attenuating the higher frequencies using Python to modify the original wav file. My question is whether this seems like a viable solution or not? Is it possible to make up for a transfer function that is making it difficult to transmit the low frequency parts of the signal by amplifying those parts of the signal in the file to be transmitted?
Here is the GnuRadio flowchart I'm using for the USRP transmission: