CODEWITHSUNDEEP
javaaudiosignal-processingfft
Yuriy Kravets
Yuriy Kravets

Reputation: 1263

Distinguish notes FFT algorithm

What I am trying to achieve is distinguishing separate notes in an audio file. For simplicity lets say that a couple of notes are played one after another. The main question is how to determine when the next note is played ?
What I have already done is reading samples from an audio file and doing Fourier Transform on those samples using JTransforms library. Here's what I get:
piano note E.
Then I have calculated spectrum based on the data that FFT returned, and here's what I get:
piano note E.
As I understand the bigger "columns" on the chart are the harmonics, and the small ones are noise and other non-harmonic overtones, right ?

After that I have tried to do same process with audio file with two notes played one after another, but the result was kind of the same.

As a side question, do any of you know some lightweight and fast libraries for visualizing such data ? Because using JFreeChart for bigger datasets is a real pain for my processor.

Upvotes: 0

Views: 1047

Answers (1)

hotpaw2
hotpaw2

Reputation: 70733

To detect successive frequency bursts of different frequencies, and some of their time domain parameters, one can use overlapping short FFT windows (length shorter than the expected burst length) and look for where the relative magnitudes of frequency peaks swap order, or fall above/below thresholds. If you know, a priori, the frequencies involved, you can use the Goertzel filters instead of FFTs, with sliding windows or successive approximation in time for finer time domain granularity.

For pitched notes (such as music), one can do something similar, except using a pitch detection/estimation method (instead of simple FFT magnitudes, which are not reliable) on sufficiently short time domain windows of data.

Upvotes: 1

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