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copied!<p>Sounds like a fun project.</p> <p>You can implement low-pass filters by "blurring" across samples, and high-pass by other simple maths (can't remember what that is at the moment)</p> <p>However, if you are working with audio, you will eventually want to convert signals to frequency domain and back. The best open-source library for this is FFTW3, and there is a Ruby binding in the gem <code>fftw3</code> - it works with <code>narray</code> which if you ware not already using you should consider anyway since it will perform very well on manipulating arrays of 1000s of individual samples.</p> <p>To get started converting to frequency domain:</p> <pre><code>require 'narray' require 'fftw3' # You'll need to feed in real-world data in audio_segment # This generates white noise -1.0 to 1.0 audio_segment = 2.0 * ( NArray.float(1024).random() - 0.5 ) # To avoid edges of the window looking like high-frequency changes, # you need to apply a window function. This is just a multiplier for each sampel point # Look up Hann window on Wikipedia, the maths is very simple. # hann_window is a simple 1024 NArray of floats, and you can re-use the same one each time audio_window = audio_segment * hann_window # This does FFT magic frequency_domain_window = FFTW3.fft(audio_window, -1) # What you do next depends on the processing you need to do. Typically you'll want to # re-normalise the data (as FFTW doesn't do that for you) frequency_domain_window *= 1.0/1024 # This is a very crude "notch filter" that reduces amplitude of some mid frequencies frequency_domain_window[100..200] *= 0.3 # Convert back to samples in time (but we still are in a Hann window) processed_audio_window = (FFTW3.ifft( frequency_domain_window, 0 )).real # Next you need to do an inverse of the Hann window # After then you'll want to step forward say 256 samples, and repeat the process # whilst averaging windows together where they overlap . . . </code></pre> <p>Sorry this is not a full-featured piece of code, but hopefully gives you enough pointers to go play!</p>

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