hit song science is not yet a science
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
HIT SONG SCIENCE IS NOT YET A SCIENCE
François Pachet
Pierre Roy
Sony CSL
pachet@csl.sony.fr
Sony CSL
roy@csl.sony.fr
ABSTRACT
We describe a large-scale experiment aiming at validating
the hypothesis that the popularity of music titles can be
predicted from global acoustic or human features. We use
a 32.000 title database with 632 manually-entered labels
per title including 3 related to the popularity of the title.
Our experiment uses two audio feature sets, as well as the
set of all the manually-entered labels but the popularity
ones. The experiment shows that some subjective labels
may indeed be reasonably well-learned by these
techniques, but not popularity. This contradicts recent and
sustained claims made in the MIR community and in the
media about the existence of “Hit Song Science”.
1.
INTRODUCTION
Claims have recently been formulated about the
possibility of a “Hit Science” that aims at predicting
whether a given cultural item, e.g. a song or a movie, will
be a hit, prior to its distribution. Such claims have been
made in the domains of music [4] as well as movie [7],
and are the basis of hit counseling businesses [9], [17].
More precisely, the claim is that cultural items would
have specific, technical features that make them preferred
by a majority of people, explaining the non uniform
distribution of preferences [6]. These features could be
extracted by algorithms to entirely automate the prediction
process from a given, arbitrary new item (a song or a
movie scenario).
A study showed the inherent unpredictability of
cultural markets [19]. The unpredictability was shown to
stem from a cumulative advantage or rich-get-richer
effect. The study did not conclude, however, that there
was no objective substrate to user preferences, but
demonstrated the existence of a preference bias introduced
when users are exposed to judgments of their pairs.
This study assesses to which extent this claim is
scientifically grounded in the domain of music, i.e. can we
extract automatically features accounting for song
popularity, regardless of the cultural biases evidenced
by [19].
In particular, [4] describe an experiment in which a
system is trained to learn a mapping between various
musical features extracted from the acoustic signal and
from the lyrics, and the popularity of the song. They
conclude from this experiment that their system learns
something about popularity, and so that Hit Song Science
is indeed possible.
However, the idea that popularity can be inferred from
such technical features contradicts the natural intuitions of
any musically-trained composer.
In this paper, we describe a larger-scale and more
complete experiment designed to further validate this
claim. We use a 32.000 song database of popular music
titles, associated with fine-grained human metadata, in the
spirit of the Pandora effort [16]. To ensure that the
experiment is not biased, we use three sets of different
features. We describe the various experiments conducted
and conclude that popularity is basically not learned by
any of these feature sets.
2.
EXTRACTING GLOBAL DESCRIPTORS
The most widely used approach to extract global
information from acoustic signals is to identify feature
sets supposed to be representative of musical information
contained in the signal, and to train classifiers such as
SVMs (Support Vector Machines) on manually annotated
data (Train set). These classifiers are then tested, typically
on other data sets (the Test set), and their performance is
evaluated. If the experiment is performed without biases, a
good performance of the classifier means that the feature
set considered does carry some information pertaining to
the classification problem at hand.
In this paper we describe an experiment similar in sprit
to that of [4] on a 32,000 song database. We use three
different feature sets to train our classifiers: a generic
acoustic set à la MPEG-7, a specific acoustic set using
proprietary algorithms, and a set of high-level metadata
produced by humans. These feature sets are described in
the next sections.
2.1. Generic Audio Features
The first feature set we consider is related to the so-called
bag-of-frame (BOF) approach. The BOF approach owns
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
his success to its simplicity and generality, as it can be,
and has been, used for virtually all possible global
descriptor problems. The BOF approach consists in
modelling the audio signal as the statistical distribution of
audio features computed on individual, short segments.
Technically, the signal is segmented into successive,
possibly overlapping frames, from which a feature vector
is computed. The features are then aggregated together
using various statistical methods, varying from computing
the means/variance of the features across all frames to
more complex modelling such as Gaussian Mixture
Models (GMMs). In a supervised classification context,
these aggregated features are used to train a classifier. The
BOF approach can be parameterized in many ways: frame
length and overlap, choice of features and feature vector
dimension, choice of statistical reduction methods
(statistical moments or Gaussian Mixture Models), and
choice of the classifier (Decision Trees, Support Vector
Machines, GMM classifiers, etc.). Many papers in the
MIR literature report experiments with variations on BOF
parameters on varied audio classification problems [1],
[5], [12], [15]. Although perfect results are rarely
reported, these works demonstrate that the BOF approach
is relevant for extracting a wide range of global music
descriptors.
The generic feature set we consider here consists of 49
audio features taken mostly from the MPEG-7 audio
standard [11]. This set includes spectral characteristics
(Spectral Centroid, Kurtosis and Skewness, HFC, Mel
Frequency Cepstrum Coefficients), temporal (ZCR, InterQuartile-Range), and harmonic (Chroma). These features
are intentionally chosen for their generality, i.e. they do
not contain specific musical information nor musically ad
hoc algorithms.
Various experiments [14] were performed to yield the
optimal BOF parameters for this feature set: localization
and duration of the signal, statistical aggregation operators
used to reduce dimensionality, frame size and overlap.
The best trade-off between accuracy and computation time
is achieved with the following parameters: 2048 sample
frames (at 44,100 Hz) with a 50% overlap computed on a
2-minute signal extracted from the middle part of the title,
the features are the two first statistical moments of this
distribution, i.e. the mean and variance, are considered,
yielding a total feature vector of dimension 98 (49 means
+ 49 variances).
2.2. Specific Audio Features
The specific approach consists in training the same (SVM)
classifier with a set of “black-box” acoustic features
developed especially for popular music analysis tasks by
Sony Corporation. These proprietary features have been
used in commercial applications such as hard disk based
Hi-Fi systems. Altogether, the specific feature set also
yields a feature vector of dimension 98, which guaranties
a fair comparison with the generic feature set. As opposed
to the generic set, the specific set does not use the BOF
approach: each feature is computed on the whole signal,
possibly integrating specific musical information. For
instance, one feature describes the proportion of perfect
cadences (i.e. resolutions in the main tonality) in the
whole title. Another one represents the proportion of
percussive sounds to harmonic sounds. We cannot provide
here a detailed description of these features as we are
mostly interested in comparing the performances of
acoustic classifiers on two reasonable, but different
feature sets.
2.3. Human Features
Lastly, we trained a classifier with human-generated
features. We use the 632 Boolean labels provided by our
manually annotated database (see following section) to
train the classifiers. This is not directly comparable to the
98 audio features as these labels are Boolean (and not
float values). However, as we will see, these features are
good candidate for carrying high-level and precise musical
information that are typically not well learnt from features
extracted from the acoustic signal.
3.
THE HIFIND DATABASE
3.1. A Controlled Categorization Process
Several databases of annotated music have been proposed
in the MIR community, such as the RWC database [8], the
various databases created for the MIREX tests [3].
However, none of them has the scale and number of labels
needed to test our hypothesis. For this study we have used
a music and metadata database provided by the HiFind
Company [10]. This database is a part of an effort to
create and maintain a large repository of fine-grained
musical metadata to be used in various music distribution
systems, such as playlist generation, recommendation,
advanced music browsing, etc. The HiFind labels are
binary (0/1 valued) for each song. They are grouped in 16
categories, representing a specific dimension of music:
Style, Genre, Musical setup, Main instruments, Variant,
Dynamics, Tempo, Era/Epoch, Metric, Country, Situation,
Mood, Character, Language, Rhythm and Popularity.
Labels describe a large range of musical information:
objective information such as the “presence of acoustic
guitar”, or the “tempo range” of the song, as well as more
subjective characteristics such as “style”, “character” or
“mood” of the song. The Popularity category contains
three (Boolean) labels, low, medium and high. It
represents the popularity of the title, as observed e.g. from
hit charts and records of music history. These three labels
are, in principle, mutually exclusive.
The categorization process at work at HiFind is highly
controlled. Each title is listened to entirely by one
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
categorizer. Labels to be set to true are selected using an
ad’hoc categorization software. Label categories are
considered in some specific order. Within a category,
some rules may apply that prevent some combinations of
labels to be selected. The time taken, for a trained
categorizer, to categorize a single title is about 6 minutes.
The categorized titles are then considered by a
categorization supervisor, who checks, among other
things, aspects such as consistency and coherence to
ensure that the description ontologies are well-understood
and utilized consistently across the categorization team.
Although errors and inconsistencies can be made during
this process, it nevertheless guaranties a relative good
“quality” and consistency of the metadata, as opposed for
instance to collaborative tagging approaches in which
there is no supervision. Additionally the metadata
produced is extremely precise (up to 948 labels can be
considered per title), a precision which is difficult to
achieve with collaborative tagging approaches.
There is no systematic way to ensure that the
categorization produces absolutely correct and consistent
information, so we had to consider the database as it was
provided as ground truth. Some minor “clean up” was
performed before use, by discarding titles with metadata
of obviously of low quality. For instance, we discarded
songs having much less labels set to “true” than the
average (37). Additionally, we kept only those labels for
which we had a significant amount of titles (above 20)
with the true and false values, to build training and testing
sets of sufficient size. As a result of this cleanup, the total
number of titles considered in this study is 32978, and the
number of labels 632. (Note that those labels correspond
to the 632 human features for the experiment described in
Section 2.3) Acoustic signals were given in the form of a
wma file at 128 kbps. This database was used both for
training our classifiers and for testing them, as described
in Section 4.1.
3.2. Database Redundancy
The HiFind database is sparse: the mean number of labels
set to true per song (occupation factor) is 5.8% (i.e. 37 on
a total of 632). Sparseness suggests the dominant role of
the true-valued labels compared to false-valued labels for
a given song. It is also redundant. For instance, labels
‘Country Greece’ and ‘Language Greek’ are well
correlated. This redundancy has been analyzed and
exploited for performing statistical inference, e.g. to infer
unknown attributes from a partial description of a music
title, or for suggesting modifications [18].
3.3. Assessing Classifiers
To avoid the problems inherent to the sole use of precision
or recall, the traditional approach is to use F-Measure to
assess the performance of classifiers. For a given label, the
recall is the proportion of positive examples (i.e. the
titles that are true for this label) that were correctly
predicted. The precision is the proportion of the
predicted positive examples that were correct. When the
proportion of positive examples is high compared to that
of negative examples, the precision will usually be
artificially very high and the recall very low, regardless of
the actual quality of the classifier. The F-measure
addresses this issue and is defined as:
2 However, in our case, we have to cope with a
particularly unbalanced 2-class (True and False) database.
So the mean value of the F-measure for each class (True
and False) can still be artificially good. To avoid this bias,
we assess the performance of our classifiers with the more
demanding min F-measure, defined as the minimum value
of the F-measure for the positive and negative cases. A
min-F-measure near 1 for a given label really means that
the two classes (True and False) are well predicted.
4.
EXPERIMENT
4.1. Experiment Design
We first split the HiFind database in two “balanced” parts
Train and Test, so that Train contains approximately the
same proportion of examples and counter-examples for
each labels as Test. We obtained this state by performing
repeated random splits until a balanced partition was
observed. We trained three classifiers, one for each feature
set (generic, specific and human). These classifiers all
used a Support Vector Machine (SVM) algorithm with a
Radial-Basis Function (RBF) kernel, and were trained and
tested using Train and Test. More precisely, each
classifier, for a given label, is trained on a maximally
“balanced” subset of Train, i.e. the largest subset of Train
with the same number of “True” and “False” titles for this
label (popularity Low, Medium and High). In practice the
size of these individual train databases varies from 20 to
16320. This train database size somehow represents the
“grounding” of the corresponding label. The classifiers are
then tested on the whole Test base. Note that the Test base
is usually not balanced with regards to a particular label,
which justifies the use of the min-F-measure to assess the
performance of each classifier.
4.2. Random Oracles
To assess the performance of our classifiers, we compare
them to that of random oracles defined as follows: given
an label with p positive examples (and therefore N-p
negative ones, with N the size of the test set), this oracle
returns true with a probability p/N.
By definition, the min-F-measure of a random oracle
only depends on the proportion of positive and negative
examples in the test database.
For instance, for a label with balanced positive and
negative examples, the random oracle defined as above
has a min-F-measure of 50%. A label with 200 positive
examples (and therefore around 16,000 negative
examples) leads to a random oracle with a min-F-measure
of 2.3%. So the performance of the random oracle is a
good indicator of the size of the train set, and can
therefore be used for comparing classifiers as we will see
below.
4.3. Evaluation
Classifiers
the
Performance
of
2.5
R² = 0.797
2
1.5
R² = 0.7768
1
0.5
Acoustic
0
0
Comparison with random oracles
The comparison of the performance of acoustic classifiers
with random oracles shows that the classifiers do indeed
learn something about many of the HiFind labels. More
than 450, out of 632, are better learned with the acoustic
classifiers than with our random oracle. Table 1 indicates,
for each feature set, the distribution of the relative
performances of acoustic classifiers with regards to
random oracles.
Improvement
Specific
Generic
50
8
0
40
12
15
30
43
20
20
111
79
10
330
360
0
128
158
Table 1. Number of labels for which an acoustic classifier
improves over a random classifier by a certain amount.
Column “Improvement” reads as follows: there are 111
labels for which a specific acoustic classifier outperforms
a random classifier by +20 (in min-F-measure).
Table 1 also shows that around 130 to 150 labels lead
to low-performance classifiers, i.e. acoustic classifiers that
do not perform significantly better than a random oracle
(the last row of the table); approximately half of the labels
lead to classifiers that improve over the performance of a
random classifier by less than 10; the rest (top rows)
clearly outperform a random oracle, i.e. they are wellmodeled by acoustic classifiers.
0.5
1
1.5
2
min-F-measure (log scale)
Generic
Specific
Regression (generic)
Regression (specific)
Figure 1. Log-log graph of the distribution of the
performance of acoustic classifiers for both feature sets.
This distribution of the performance of classifiers is close
to a power law.
These power laws suggest that a natural organization
process is taking place in the representation of human
musical knowledge, and that the process of automatic
audio classification maintains this organization.
4.3.3. Specific features slightly outperform generic
features
Not surprisingly, we can see that specific features perform
always better than the generic ones. This is illustrated by
Figure 2. Since the classifiers are both based on the same
SVM/kernel, the difference can only come from 1) the
actual features extracted or 2) the aggregation method. For
the generic features, the aggregation is based on means
and averages over all the segments of the song. For the
specific features, the aggregation is ad hoc.
Number of acoustic classifiers
4.3.1.
of
number of classifiers (log scale)
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
600
500
400
300
200
100
Performance of acoustic classifier (min-F-measure)
4.3.2. Distribution
classifiers
of
performances
for
acoustic
At this point, it is interesting to look at the distribution of
the performances of these acoustic classifiers. These
performances vary from 0% for both feature sets to 74%
for the generic features and 76% for the specific ones. The
statistical distribution of the performances is close to a
power law distribution, as illustrated by the log-log graph
of Figure 1.
0
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70 75
Specific
Generic
Figure 2. Cumulated distribution of the performance of
acoustic classifiers for the generic and specific feature
sets. There are more classifiers with low performance for
the generic feature sets (leftmost side of the graph).
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
10.0
5.0
Number of training samples
0.0
Specific
Generic
Figure 3. The relative performances of the 632 acoustic
classifiers (i.e. the difference between the min-F-measures
of the classifier and of the corresponding random oracle)
for specific and generic features, as a function of the
training database size. The performance of the acoustic
classifiers increases with the size of the training database.
These experiments show that acoustic classifiers
definitely learn some musical information, with varying
degrees of performance. It also shows that the subjective
nature of the label do not seem to influence their capacity
to be learned by audio features. For instance, the label
“Mood nostalgic” is learnt with the performances of 48%
(specific features), and 43% (generic features), to be
compared to the 6% of the random oracle. Similarly, label
“Situation evening mood” is learnt with 62% and 56%
respectively, against 36% for random. So popularity is, a
priori, a possible candidate for this task.
4.4. Inference from Human Data
This double feature experiment is complemented by
another experiment in which we train a classifier using all
the HiFind labels but the Popularity ones. This is justified
by the low entropy of the database as discussed in Section
3.2. Contrarily to the acoustic classifiers, we do not
present here the performances of the classifiers for all
HiFind labels. Indeed, some pairs of HiFind labels are
perfectly well correlated so this scheme works perfectly
for those, but this result is not necessarily meaningful (e.g.
to infer the country from the language). The same Train /
Human
features
Dumb
features
Random
oracle
15.0
Popularity labels are
Corrected
specific
20.0
The results concerning the
summarized in Table 2.
Specific
features
25.0
4.5. Summary of Results for Inferring Popularity
Generic
features
Classifier performance (min-F-measure)
Lastly, we can observe the relationship between the
performance and the size of the training set. The trend
lines in Figure 3 show that the performances of acoustic
classifiers increase with the training dataset size,
regardless of the feature set. This is consistent with the
acknowledged fact that machine-learning algorithms
require large numbers of training samples, especially for
high-dimensional feature sets.
Test procedure described above applied with the 629 nonpopularity labels as input yields the following result (minF-measure): 41% (Popularity-Low), 37% (PopularityMedium) and 3% (Popularity-High).
Popularity
label
4.3.4. Acoustic classifiers perform better for large
training sets
Low
Medium
High
36
36
4
35
34
3
31
38
3
41
37
3
32
28
3
27
22
3
Table 2. The performances (min-F-measures) of the
various classifiers for the three Popularity labels. No
significant improvement on the random oracle is
observed.
These results show clearly that the Popularity category
is not well-modeled by acoustic classifiers: its mean
performance is ranked fourth out of 16 categories
considered, but with the second lowest maximum value
among categories.
Although these performances appear to be not so bad at
least for the “Low” label, the comparison with the
associated random classifiers shows that popularity is in
fact practically not learnt. Incidentally, these
performances are not improved with the correction
scheme, a method that exploits inter-relations between
labels to correct the results [14], in the spirit of the
contextual approach described in [2].
Interestingly, the use of human features (all HiFind labels)
does not show either any significant performance.
Lastly, we also considered a priori irrelevant
information to train our classifiers: the letters of the song
title, i.e. a feature vector of size 26, containing the number
of occurrences of each letter in the song title. The
performances of the corresponding classifiers are
respectively 32% 28% and 3% (for the low, medium and
high popularity labels, see Table 2). This shows that even
dumb classifiers can slightly improve the performances of
random classifiers (by 5% in this case for the medium and
low popularity labels), but that this information does not
teach us anything about the nature of hits.
These results suggest that there are no significant
statistical patterns concerning popularity using these
features sets.
5.
CONCLUSION
We have shown that the popularity of a song cannot be
learnt by using state-of-the-art machine learning
Pachet, F. and Roy, P. “Hit Song Science is Not yet a Science”, Proc. of Ismir ‘08, Philadelphia, pp. 355-360
techniques with two sets of reasonable audio features.
This result is confirmed when using supposedly higherlevel human metadata. This large-scale evaluation, using
the best machine-learning techniques available to our
knowledge, contradicts the claims of “Hit Song Science”,
i.e. that the popularity of a music title can be learned
effectively from known features of music titles, either
acoustic or human. We think that these claims are either
based on spurious data or on biased experiments. This
experiment is all the more convincing that some other
subjective labels can indeed be learnt reasonably well
using the features sets described here (e.g. the “mood
nostalgic” label).
This experiment does not mean, however, that
popularity cannot be learnt from the analysis of a music
signal or from other features. It rather suggests that the
features used commonly for music analysis are not
informative enough to grasp anything related to such
subjective aesthetic judgments. Current works are in
progress to determine “good features” using feature
generation techniques [13], which have been shown to
outperform manually designed features for specific
analysis tasks. However, more work remains to be done to
understand the features of subjectivity for even simpler
musical objects such as sounds or monophonic melodies.
Hit song science is not yet a science, but a wide open
field.
6.
ACKNOWLEDGEMENT
This research has been partly supported by the TAGora
project funded by the Future and Emerging Technologies
program(IST-FET) of the European Commission under
the contract IST-34721. The information provided is the
sole responsibility of the authors and does not reflect the
Commission's opinion. The commission is not responsible
for any use that may be made of data appearing in this
publication.
[5] Essid, S. Richard, G. and David, B. Instrument
Recognition in Polyphonic Music Based on
Automatic Taxonomies, IEEE Trans. on Speech,
Audio and Lang. Proc., 14(1), 68-80, 2006.
[6] Frank, R. H. Cook, P. J. The Winner-Take-All
Society, Free Press, New York, NY, 1995.
[7]
Gladwell, M. The Formula. The New Yorker, 2006.
[8] Goto, M. Hashigushi, H., Nishimura, T., Oka, R.
“RWC Music Database: Popular, Classical and Jazz
Music Databases”, Proc. of Ismir 2002, Paris,
France.
[9]
http://www.hitsongscience.com
[10] http://www.HiFind.com
[11] Kim, H. G. Moreau, N. Sikora, T. MPEG-7 Audio
and Beyond: Audio Content Indexing and Retrieval,
Wiley & Sons, 2005.
[12] Liu, D. Lu, L. Zhang, H.-J. Automatic mood
detection and tracking of music audio signals. IEEE
Trans. on Speech Audio and Language Processing,
14(1), pp 5-18, 2006.
[13] Pachet, F. and Roy, P. Exploring billions of audio
features. In Eurasip, editor, Proc. of CBMI 07,
Bordeaux, France.
[14] Pachet, F. and Roy, P. Improving Multi-Label
Analysis of Music Titles: A Large-Scale Validation
of the Correction Hypothesis, submitted to IEEE
TALSP, 2008.
[15] Pampalk, E., Flexer, A., Widmer G. Improvements of
Audio-Based Music Similarity and Genre
Classification, pp. 628-633, Proc. of Ismir 2005,
London, UK.
[16] http://www.pandora.com
[17] http://www.platinumblueinc.com/
7.
REFERENCES
[1] Aucouturier, J.-J. and Pachet, F. Improving Timbre
Similarity: How high is the sky? J. of Negative
Results in Speech and Audio Sciences, 1(1), 2004.
[2] Aucouturier, J.-J., Pachet, F., Roy, P. and Beurivé, A.
Signal + Context = Better Classification. Proc. of
Ismir 2007, Vienna, Austria.
[3] Cano, P. Gómez, E. Gouyon, F. Herrera, P.
Koppenberger, M. Ong, B. Serra, X. Streich, S.
Wack, N. (2006). ISMIR 2004 Audio Description
Contest, MTG Technical Report: MTG-TR-2006-02.
[4] Dhanaraj, R. and Logan, B. Automatic Prediction of
Hit Songs, Proc. of Ismir 2005, London, UK.
[18] Rabbat, P. and Pachet, F. Statistical Inference in
Large-Scale Databases: How to Make a Song Funk?
Proc. of Ismir 2008, Philadephia, USA.
[19] Salganik, M. J. Dodds, P. S. Watts, D. J.
Experimental
Study
of
Inequality
and
Unpredictability in an Artificial Cultural Market,
Science, 311, 854-856, 2006.
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF

advertising