I am using an FFT package (GFT) to analyze a signal from a pressure sensor. I am unsure of the results I am getting, so I decided to try to verify the FFT package using a known input. I am using a signal generator to produce a sine wave of +/- 5V @ 5 and 100 Hz. When I run the FFT on the data @ 5 Hz, the results show a peak amplitude of about 2.3 V @ 5 Hz. The max voltage from the sampled data was about 4.2 V. When I run the FFT on the data @ 100 Hz, the results show a peak amplitude of about 1.7 V @ 100 Hz. Max voltage from the sampled data was about 4.9 V. What results should I be seeing from the FFT analysis? I thought that if I input sine wave data at a certain peak voltage and frequencey that the FFT results would show that same peak voltage and frequency (i.e. 5 V @ 5 Hz in would give me an FFT result of 5 V @ 5 Hz in the frequency domain). Also, somebody mentioned that I might get a result of (amplitude/2) from the FFT depending on the FFT routine. What does this mean? Is that dependent on the algorithm that is used? I heard the terms 'peak to peak' and 'peak' used in reference to this. What does this mean?