Calculating the Beat/Minute in a Audio File in Android [closed]

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I want to calculate the beat per minute in a Audio File in android , I have just a small clue , There is a Visualizer Library which creates a DIGITAL BAR effect with the Audio files wave , I can check for the beat with this , Is this the correct solution or is there any proper way to do this ? I want to categorize Audio files in a proper way. According to the Beat/minute in a File.

Any help would be greatfull

Answer 1

Beats per minute can be calculated with multiple levels, a simple energy calculator which you are referring to by the should level meter or VAD (voice/ audio activity detector) can be somewhat simple to make, where as a proper pitch detector, this is a complex process and isolating the beat of music segment can be complex since perception of a beat is complex. If you are simply interested in energy calculator/ beat like feature what you can do is have a two running averages and see how large is your signal relative to the other.

X= [x1……xn] input audio samples, separate the buffers into smaller segment say 100 samples. n=100,  
Take the absolute value for this array abs(X), 
Simple one pole smoothing function can be made with
X_filtered_long= X_filtered_long . (1-alpha) + abs(X). alpha // alpha is .02, value depends on the sample rate, signals and what beat of interest 
Create the second filtered signals 
X_filtered_short= X_filtered_short . (1-beta) + abs(X). beta // beta is .2 
If (X_filtered_short > X_filtered_long) 

Detected_beat= 1; 
InsideBeat=+1;

else 

Detected_beat= 0;
InsideBeat=0;

If you want to, "I want to categorize Audio files in a proper way. According to the Beat/minute in a File." This can only be done with finger printing the audio with parameters such as MFCC. Good reference would be

Automatic genre classification of music content: a survey
Scaringella, N. ; Zoia, G. ; Mlynek, D.
Signal Processing Magazine, IEEE
Volume: 23 , Issue: 2

Answer 2

What you're asking here is tremendously difficult.

Audio analysis to get the beats is usually done with complex mathematical manipulation of the audio data, by transforming the audio signal from the time-domain to the frequency-domain using signal-processing techniques. There are whole books dedicated to this subject.

Visualizers like the one you mention internally use many of these DSP techniques and it would probably be an even worse nightmare to analyze the visualizer data than the audio data.

Even if you manage to find a library that does this for you, the results would be very unreliable. Maybe for electronic music where the beats are more obvious you would get better results than for classical music or jazz.