Fast Fourier Transform to View Audio Frequency Spectrum

Fast Fourier Transform Wiki notes
What is Fourier Transform?

Or if you are in school and your laboratory includes a frequency analyzer equipment; try running any time-domain signal into it (such as sine wave tone).Then confirm the graph and understand the relationships between a time-domain function to its frequency domain equivalent.

Most engineering students might perform this experiment. You also need an oscilloscope to view the waveform of a time domain signal. If you using some audio software with FFT capabilities (such as Audacity), you can see their differences below:

Time domain waveform of a 440Hz sine wave:

Sine wave tone 400Hz

Sine wave tone 400Hz

Frequency domain waveform of a 440Hz sine wave:

Sine wave tone 400Hz

Sine wave tone 400Hz

Best practices on using FFT Frequency Spectrum Analysis

1.) For best accuracy, always use the highest possible FFT size. In Adobe Audition 1.5, the highest possible is 65536.

2.) For best real time frequency domain representation (if you would like to see a real time plot of frequency vs amplitude when an audio is being played) you will need to set it at FFT size of 1024.

3.) If you have options in your FFT, you can start with the Blackmann-Harris algorithm.

4.) You can also use free software like Audacity as it includes a FFT frequency spectrum feature. In Windows 7 Audacity version 1.3 Beta, you simply need to go to Analyze — Plot spectrum. In there you can adjust the FFT settings, algorithm, etc.

5.) Never rely on FFT spectrum graph alone in your audio mixing and mastering activities. You need to use your ears and other tools to come up with the desired audio mixing settings. I recommend you read the following tutorials for additional information:

AudioSpectro FIRE– A tool for attaining frequency balance in audio mastering.

Basics on frequency analysis – a tutorial with emphasis on analyzing audio waveforms during mixing.

6.) Use FFT spectrum analysis to confirm EQ corrections and filtering. Although the ears can be a very accurate instrument in a highly precise monitoring environment; it is smart to double check the effect of EQ adjustments by examining the frequency spectrum.

Content last updated on July 4, 2012