Posts Tagged python

The Echo Nest Remix SDK

One of the joys of working at the Echo Nest is the communal music playlist.  Anyone can add, rearrange or delete music from the queue.  Of course, if you need to bail out (like when that Cindi Lauper track is sending you over the edge) you can always put on your headphones and tune out the mix.   The other day,  George Harrison’s “Here Comes the Sun” started playing, but this was a new version – with a  funky drum beat, that I had never heard before – perhaps this was a lost track from the Beatle’s Love?  Nope, turns out it was just Ben, one of the Echo Nest developers, playing around with The Echo Nest Remix SDK.

The Echo Nest Remix  SDK is an open source Python library that lets you manipulate music and video.  It sits on top of the Echo Nest Analyze API, hides all of the messy details of sending audio back to the Echo Nest, and parsing the   XML response, while still giving  you access to the full power of the API.

remix – is one of The Echo Nest’s secret weapons – it gives you the ability to analyze and manipulate music – and not just audio manipulations such as filtering or equalizing, but the ability to remix based on the hierarchical structure of a song.  remix sits on top of a very deep analysis of the music that teases out all sorts of information about a track.  There’s high level information such as the key, tempo time signature, mode (major or minor) and overall loudness.   There’s also information about the song structure.  A song is broken down into sections (think verse, chorus, bridge, solo),  bars, beats, tatums (the smallest perceptual metrical unit of the song) and segments (short, uniform sound entities).  remix gives you access to all of this information.

I must admit that I’ve been a bit reluctant to use remix – mainly because after 9 years at Sun Microsystems I’m a hard core Java programmer (the main reason I went to Sun in the first place was because I liked Java so much).  Every time I start to use Python I get frustrated because it takes me 10 times longer than it would in Java. I have to look everything up.  How do I concatenate strings? How do I find the length of a list? How do I walk a directory tree?   I can code so much faster in Java. But … if there was ever a reason for me to learn Python it is this remix SDK.  It is just so much fun – and it lets you do some of the most incredible things.  For example, if you want to add a cowbell to every beat in a song, you can use  remix  to get the list of all of the beats (and associated confidences)  in a song, and simply overlap a cowbell strike at each of the time offsets.

So here’s my first bit of Python code using  remix. I grabbed one of the code samples that’s included in the distribution, had the aforementioned Ben spend two minutes walking me through the subtleties of Audio Quantum and I was good to go.    My first bit of code just takes a song and swaps beat two and beat three of all measures that have at least 3 beats.

def swap_beat_2_and_3(inputFile, outputFile):
    audiofile = audio.LocalAudioFile(inputFile)
    bars = audiofile.analysis.bars
    collect = audio.AudioQuantumList()
    for bar in bars:
        beats = bar.children()
        if (len(beats) >= 3):
            (beats[1], beats[2]) = (beats[2], beats[1])
        for beat in beats:
            collect.append(beat);
    out = audio.getpieces(audiofile, collect)
    out.encode(outputFile)

The  code analyzes the input, iterates through the bars and if a bar has more than three beats, swaps them. (I must admit, even as a hard core Java programmer, the ability to swap things with (a,b) = (b,a) is pretty awesome) and then  encodes and writes out a new audiofile.   The resulting audio is surprisingly musical. Here’s the result as applied to Maynard Ferguson’s “Birdland”:

(and speaking of cool, Soundcloud is a great place to post these remixes, it lets anyone attach a comment at any point in time on a track).

This is just great programming fun.  I think I’ll be spending my spare coding time learning more Python so I can explore all of the things one can do with remix.

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