Matlab Introduction

This code provides a quick introduction to the Million Song Dataset and how to access and manipulate it from Matlab. For more information and other tutorials see the Million Song Website http://millionsongdataset.com.

This tutorial shows the basic access of the per-track data record from within Matlab, and also shows how to use the provided SQLite databases to search the metadata.

Contents

Setup

Before running this tutorial, you must complete the following setup steps:

(1) Obtain the Million Song Dataset, or Million Song Subset. This demo is based on the Subset, but the commands are identical for the full set. You can download the Subset (2.8 GB) directly from http://millionsongdataset.com/pages/getting-dataset . We assume this file has been decompressed to the directory MillionSongSubset/ in the current directory (or modify code below).

(2) Obtain the sample codebase. You can download this from https://github.com/tb2332/MSongsDB . We assume the entire tree has been decompressed into MSongsDB/ .

(3) Obtain the Matlab SQLite interface mksqlite, available from http://developer.berlios.de/projects/mksqlite/ . We assume this has been unpacked into mksqlite/ .

Now we can make sure the SQLite interface is compiled, and the paths are set up:

% Compile mksqlite (only needs to be done once)
cd mksqlite
buildit

compiling release version of mksqlite...
completed.

cd ..
% add mksqlite to the path
addpath('mksqlite');

% set up Million Song paths
global MillionSong MSDsubset
MillionSong ='MillionSongSubset';  % or 'MillionSong' for full set
msd_data_path=[MillionSong,'/data'];
msd_addf_path=[MillionSong,'/AdditionalFiles'];
MSDsubset='subset_'; % or '' for full set
msd_addf_prefix=[msd_addf_path,'/',MSDsubset];
% Check that we can actually read the dataset
assert(exist(msd_data_path,'dir')==7,['msd_data_path ',msd_data_path,' is not found.']);

% path to the Million Song Dataset code
msd_code_path='MSongsDB';
assert(exist(msd_code_path,'dir')==7,['msd_code_path ',msd_code_path,' is wrong.']);
% add to the path
addpath([msd_code_path,'/MatlabSrc']);

Simple file access

The Million Song Dataset stores the Echo Nest Analyze features and meta data for each track in its own HDF5 data file, organized into file hierarchy based on the Echo Nest hash codes. First, we build a list of all h5 files under our data tree. Then we load one file, look at the methods available, and plot the chroma for the first part of the file.

% Build a list of all the files in the dataset
all_files = findAllFiles(msd_data_path);
cnt = length(all_files);
disp(['Number of h5 files found: ',num2str(cnt)]);

% Get info from the first file using our wrapper
h5 = HDF5_Song_File_Reader(all_files{1});
disp(['artist name is: ',h5.get_artist_name()]);
disp([' song title is: ',h5.get_title()]);

Number of h5 files found: 10000
artist name is: Casual
 song title is: I Didn't Mean To

% Show all the available methods
methods('HDF5_Song_File_Reader')

Methods for class HDF5_Song_File_Reader:

HDF5_Song_File_Reader           get_loudness                    
delete                          get_mode                        
get_analysis_sample_rate        get_mode_confidence             
get_artist_7digitalid           get_num_songs                   
get_artist_familiarity          get_release                     
get_artist_hotttnesss           get_release_7digitalid          
get_artist_id                   get_sections_confidence         
get_artist_latitude             get_sections_start              
get_artist_location             get_segments_confidence         
get_artist_longitude            get_segments_loudness_max       
get_artist_mbid                 get_segments_loudness_max_time  
get_artist_mbtags               get_segments_loudness_start     
get_artist_mbtags_count         get_segments_pitches            
get_artist_name                 get_segments_start              
get_artist_playmeid             get_segments_timbre             
get_artist_terms                get_similar_artists             
get_artist_terms_freq           get_song_hotttnesss             
get_artist_terms_weight         get_song_id                     
get_audio_md5                   get_start_of_fade_out           
get_bars_confidence             get_tatums_confidence           
get_bars_start                  get_tatums_start                
get_beats_confidence            get_tempo                       
get_beats_start                 get_time_signature              
get_danceability                get_time_signature_confidence   
get_duration                    get_title                       
get_end_of_fade_in              get_track_7digitalid            
get_energy                      get_track_id                    
get_key                         get_year                        
get_key_confidence              

% .. covers all the EN Analyze API fields

% Plot the first 200 chromas
chromas = h5.get_segments_pitches();
subplot(311)
imagesc(chromas(:,1:200))
axis xy
colormap(1-gray)
colorbar
title('first 200 chromas');

Resynthesis

The EN Analyze features provide only a simplified description of the original audio; however, it's possible to reconstruct an approximation of the original audio by combining the chroma, timbre, and level features. We've implemented a rough stab at this.

% Resynthesize the first 30 seconds using chroma and timbre
sr = 16000;
dur = 30; % first 30s
x = en_resynth(h5,dur,sr);
% Take a listen
soundsc(x,sr);
% recognizable?
% Plot the spectrogram, for comparison
subplot(312)
specgram(x,512,sr);
caxis(max(caxis)+[-80 0]);

Mapping over all the data files

Many applications require searching over all the data files. With a million tracks, this can take some time. Even with the subset (10,000 tracks, or 1% of the database), it takes a while: on a Macbook Pro, each HDF5 file access takes around 30ms, so accessing 10,000 takes on the order of 5 minutes. Here we do this, simply collecting the artist name for each track into a cell array with 10,000 entries.

% Get all artist names by mapping a function to return artist names
% over the cell array of data file names
tic;
all_artist_names = cellfun(@(f) get_artist_name(HDF5_Song_File_Reader(f)), ...
                           all_files, 'UniformOutput', false);
tend = toc;
disp(['All names acquired in ',num2str(tend),' seconds.']);
disp(['First artist name is: ',all_artist_names{1}]);
disp(['There are ',num2str(length(unique(all_artist_names))), ...
      ' unique artist names']);
% takes around 5 min on MacBook Pro to scan 10k files (30ms/file)

All names acquired in 271.083 seconds.
First artist name is: Casual
There are 4412 unique artist names

SQLite Database Access

Linear search over the files is evidently a painful process; extrapolating even the simple access above to 1M songs would take over 8 hours. To avoid this for simple access of the metadata, we have pre-built SQLite databases containing the main metadata fields (Artist name, track name, release, MusicBrainz IDs, year of release, etc.). These are conveniently accessed via the mksqlite function.

Let's try getting all the artist names again, using SQLite:

% Track metadata database
sqldb = [msd_addf_prefix,'track_metadata.db'];
% Open connection
mksqlite('open',sqldb);

mksqlite Version 1.9 build:28, an interface from MATLAB to SQLite
(c) 2008/2009 by Martin Kortmann <mail@kortmann.de>
based on SQLite Version 3.7.4 - http://www.sqlite.org

% Run the SQL query.  DISTINCT means we only get the unique names
artist_names = mksqlite('SELECT DISTINCT artist_name FROM songs');
% Close the connection (clean up)
mksqlite('close');
disp(['Found ',num2str(length(artist_names)),' distinct artist names']);
disp('First artist names are:');
for k=1:5;
    disp(artist_names(k).artist_name);
end

Found 4412 distinct artist names
First artist names are:
!!!
(hed) p.e.
089 Clique feat. Minnesota Snipe & Skinny Cueball
089 Clique feat. Prophet
1. Futurologischer Congress

% Note that some artist have many artist names, usually when a song is
% 'featuring someone else'. Therefore, we should work with artist IDs.
% Find the artist ID (and name) for the artist with the most songs in
% the dataset.
mksqlite('open',sqldb);
res = mksqlite(['SELECT DISTINCT artist_id,artist_name,Count(track_id) ' ...
                'FROM songs GROUP BY artist_id']);
mksqlite('close');
disp('Got entries that looks like:');
res(1)

Got entries that looks like:

ans = 

          artist_id: 'AR009211187B989185'
        artist_name: 'Carroll Thompson'
    Count(track_id): 2

% Sort the results
[unused, order] = sort(arrayfun(@(x)getfield(x, ...
    'Count(track_id)'),res(:)),'descend');
res = res(order);
disp('Artist with the most songs is:');
res(1)

Artist with the most songs is:

ans = 

          artist_id: 'AROIHOI122988FEB8E'
        artist_name: 'Mario Rosenstock'
    Count(track_id): 13

% finally, get all songs for that artist
mksqlite('open',sqldb);
res2 = mksqlite(['SELECT track_id title FROM songs WHERE artist_id='''...
                res(1).artist_id,'''']);
mksqlite('close');
disp(['Found ',num2str(length(res2)),' tracks for ',res(1).artist_name]);
disp(['First one is: ',res2(1).track_id,' ',res2(1).title]);

Found 13 tracks for Mario Rosenstock
First one is: TRBGYGQ128F428B0B0 Fast Eddie

Accessing 7digital Previews

Although full audio for the database is not available, each track includes a 7digital track id, which can be used to retrieve a preview (usually 30 s) via the 7digital.com API. To access the API, you have to sign up at: http://access.7digital.com/partnerprogram . You'll get your own oauth_consumer_key (for free), which you'll have to insert in the code below.

The code to read the previews into Matlab also relies on access to the command-line program "wget" via Matlab's system() call, and thus will only work on Mac/Linux systems that have this program installed.

It further relies on a working installation of mp3read, see http://labrosa.ee.columbia.edu/matlab/mp3read.html .

Here, we listen to the 7digital preview and the resynthesis from the Echo Nest features side-by-side.

% Choose a nice, melodius Dixie Chicks track.
% (we use a convenience wrapper with the SQLite data file name
% hard-coded inside)
res = msd_sql('SELECT * FROM songs WHERE title=''Lullaby'' AND artist_name=''Dixie Chicks''');

returned 1 results

% Load the 7digital preview
oauth_consumer_key='XXXXXXXXXX'; % Insert your real key HERE!
[d,sr] = msd_load_preview(res.track_id, oauth_consumer_key);
% Convert the audio to mono & dowsample
d = resample(mean(d,2),1,4);
sr = sr/4;
% Now, resynth from the features
x = en_resynth(res.track_id,0,sr);
% The previews generally start about 30s into the track.  This
% sounds about right:
soundsc([x(round(30.1*sr)+[1:length(d)],:),500*d],sr)

Acknowledgment

This material is based in part upon work supported by the National Science Foundation under Grant No. IIS-0713334. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the sponsors.

Last updated: $Date: 2011/01/27 19:56:58 $

Dan Ellis dpwe@ee.columbia.edu

Thierry Bertin-Mahieux tb2332@columbia.edu

Published with MATLAB® 7.11