Here are some additional notes:
- All audio recordings are influenced by the receive passband and audio filtering of my SB-104A
- A local peak appears around 3 kHz in all graphs. This is a birdie in my receiver and should be ignored.
- Each horizontal line represents a 3 dB amplitude step -- a factor of 2 power ratio
- Each graph is the result of FFT analysis of the speech sample that was recorded, and the frequency content varies according to what slice of time you choose to analyze. Speech is a complex, continuously changing waveform. Pure, steady tones would give more consistent results.
- My software can present a real-time FFT of the audio as it plays. In that case the frequency display varies continuously as expected for a complex, continuously changing waveform.
- Increasing the FFT size from the 1024 used in these graphs to higher numbers (2048, 4096, etc.) reveals increasingly fine details, but does not affect the overall shape of the response shown in the lowest (1024) setting.