Proceedings of the 5th International Conference on Music Information Retrieval (ISMIR 2004),
pp.403-408, October 2004.

SPEECH-RECOGNITION INTERFACES FOR MUSIC INFORMATIONRETRIEVAL: “SPEECH COMPLETION” AND “SPEECH SPOTTER”
Masataka Goto† , Katunobu Itou‡ , Koji Kitayama†† , and Tetsunori Kobayashi††National Institute of Advanced Industrial Science and Technology (AIST), Japan‡††
Nagoya University, Japan
Waseda University, Japan†

ABSTRACTThis paper describes music information retrieval (MIR)
systems featuring automatic speech recognition. Although various interfaces for MIR have been proposed,
speech-recognition interfaces suitable for retrieving musical pieces have not been studied. We propose two different speech-recognition interfaces for MIR, speech completion and speech spotter, and describe two MIR-basedhands-free jukebox systems that enable a user to retrieve
and play back a musical piece by saying its title or theartist’s name. The first is a music-retrieval system withthe speech-completion interface that is suitable for music stores and car-driving situations. When a user can remember only part of the name of a musical piece or an
artist and utters only a remembered fragment, the system
helps the user recall and enter the name by completingthe fragment. The second is a background-music playback system with the speech-spotter interface that can enrich human-human conversation. When a user is talking to another person, the system allows the user to entervoice commands for music-playback control by spottinga special voice-command utterance in face-to-face or telephone conversations. Our experimental results from useof these systems have demonstrated the effectiveness ofthe speech-completion and speech-spotter interfaces.
Keywords: speech recognition, MIR interface, hands-free MIR,
jukebox, title and artist searchVideo demonstration: http://staff.aist.go.jp/m.goto/ISMIR2004/

1. INTRODUCTION
The purpose of this study is to build a music-retrieval
system with a speech-recognition interface that facilitates
both identification of a musical piece and music playbackin everyday life. We think a speech-recognition interface
is well-suited to music information retrieval (MIR), especially retrieval of a musical piece by entering its title or theartist’s name. At home or in a car, for example, an MIRbased jukebox system with a speech-recognition interface
would allow users to change background music just by
saying the name of a musical piece or an artist. At musiclistening stations in music stores or on karaoke machines,
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a speech-recognition interface could also help users findmusical pieces they have been looking for without using
any input device other than a microphone.
Most previous MIR research, however, has not explored how speech recognition can be used for retrievingmusic information, although various MIR interfaces using text, symbols, MIDI, or audio signals have been proposed. To retrieve a musical piece, a typical approach is
to use a text query related to bibliographic information.
This approach requires the use of hand-operated input devices, such as a computer keyboard, mouse, or stylus pen.
Another approach is to use a melody-related query given
through symbols, MIDI, or audio signals. In particular,
music retrieval through a sung melody is called query byhumming (QBH), and this approach is considered promising because it requires only a microphone and can easily
be used by a novice. However, even though this approach
uses a microphone, speech recognition of the names ofmusical pieces and artists has not been considered.
In this paper, we describe two original speechrecognition interfaces, speech completion and speechspotter, which are suitable for MIR. Using these interfaces, we have built two MIR-based jukebox systems thatallow users to find and play back a musical piece by saying its title or the artist’s name.
• Music-retrieval system with the speech-completion interface
This system enables a user to retrieve a musical pieceor a list of musical pieces by an artist even if the user
can remember only part of the name of the piece orartist. A user cannot similarly enter an incomplete
name into current speech recognizers because theserecognizers tacitly force the user to utter the entire
name carefully and precisely. Our system, on the other
hand, allows a user to enter the name by uttering a remembered fragment of it: the system can complete therest (i.e., fill in the missing part) of the partially utteredfragment.
• Music playback system with the speech-spotter interface
This system enables a user to listen to background music by uttering the name of a musical piece or artist
while talking to another person. It has been difficult touse current speech recognizers in the midst of humanhuman conversation because it is difficult to judge,
from microphone input only, whether a user is speaking to another person or a speech recognizer. Our sys-

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5th International Conference on Music Information Retrievaltem, on the other hand, allows a user to enter voicecommands for music-playback control in the midst of
face-to-face or telephone conversations: the system
can spot (identify) a special voice-command utterance
in human-human conversations without otherwise interrupting the conversations.
In the following sections, we explain both of thesespeech-capable music jukebox systems and describe theirimplementation. We then show experimental results
which have demonstrated the effectiveness of our speechrecognition interfaces.
2. MUSIC-RETRIEVAL SYSTEM WITH THE
SPEECH-COMPLETION INTERFACEIn this system, a user can retrieve a musical piece by uttering a fragment of its title or the artist’s name with anintentional filled pause (the lengthening of a vowel during hesitation). In human-human conversation, when aspeaker cannot remember the entire name of a piece oran artist and hesitates while uttering the name, a listenerwill sometimes help the speaker recall it: the listener suggests options by completing the partially uttered fragment(i.e., by filling in the rest of it). For example, whena speaker cannot remember the last part of a Japanesephrase “maikeru jakuson” (in English, “Michael Jackson”) 1
and stumbles, saying “maikeru–” 2 (in English, “Michael,uh...” or “Michael–”) with a filled pause “ru–” (“uh...” or“l–”), 3 a listener can help the speaker by asking whether
the speaker intends to say “maikeru jakuson” (“MichaelJackson”). Our system can provide this completion assistance to users.
The concept of completing a fragment is widely usedin text-based interfaces. Several text editors (e.g., Emacs)
and UNIX shells (e.g., tcsh and bash), for example, provide functions for completing the names of files and commands. These functions fill in the rest of a partially typed
fragment when a completion-trigger key (typically the Tabkey) is pressed. Completion functions for pen-based interfaces have also been proposed [1]. However, even thoughcompletion is so convenient that it often becomes indispensable to users, an effective completion function forspeech input interfaces has not been developed because
there has been no effective way to trigger the function during natural speech input and current speech recognizers
have difficulty recognizing a partially uttered fragment.
We therefore propose the speech-completion interface
which completes the names of musical pieces and artists
and displays completion candidates so that a user can select the correct one (Figures 1, 2, and 3). The most important point is that we use an intentional filled pause(a vowel-lengthening hesitation like “er...”) to trigger this1 When a foreign name like “Michael Jackson” is written or pronounced in Japanese, it is regularized to conform to the Japanese style:“maikeru jakuson.”
2 In this paper, underlining indicates that the underlined syllable isprolonged (a filled pause is uttered).
3 In Japanese, vowel-lengthening hesitations like “maikeru–” (sounding like “Michael–” in English) are very common, while inserted-filler
hesitations like “Michael, uh...” are usually used in English.

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speech-completion function. To prevent this kind of completion assistance becoming annoying, it should be invoked only when a user wants to obtain completion candidates. Because the filled pause is a typical hesitation phenomenon that indicates a user is having trouble thinkingof or recalling a subsequent word [2], its use is natural 4
and makes this speech-completion function effective andpractical.
This interface provides three benefits:
1. A user can more easily recall poorly rememberednames.
2. Less labor is needed to input a long name. For example, you can enter a song title “Supercalifragilisticexpialidocious” (a song from “Mary Poppins”) byuttering “Supercalifra–, No.1”.
3. The user is not forced to utter the entire name carefully
and precisely, as is required by most current speechrecognition systems.
2.1. Search methods
Our music-retrieval system provides two speech-based
search methods for a music database: a method of specifying the musical-piece title and a method of specifying theartist’s name. For the latter method, the system shows, on
the screen, a numbered list of titles for the specified artist
in the music database, and a user can select an appropriate
title by uttering either the title or its number (Figure 3).
After the musical piece is identified by either method, thesystem plays back its sound file in our current implementation. This interface can also be used for playing back theappropriate standard MIDI file (SMF) or karaoke track,making a play list, or editing and downloading music files.
When a user enters the names of musical pieces orartists, the system allows the user to complete speech ineither a forward or backward direction:
1. Forward speech completion (Figure 1)
A user who does not remember the last part of a namecan invoke this completion by uttering the first partwhile intentionally lengthening its last syllable (making a filled pause). Here, the user can insert a filled
pause at an arbitrary position (even within a word).
The user then gets a numbered list of completion candidates whose beginnings acoustically resemble theuttered fragment.
2. Backward speech completion (Figure 2)
A user who does not remember the first part of aname can invoke this completion by uttering the lastpart after intentionally lengthening the last syllable ofa predefined special keyword — called the wildcard
keyword (In the current implementation, we use theJapanese wildcard “nantoka” (in English, “something”),
and a user can utter, for example, “nantoka– jakuson” (“something– Jackson”) 5 ). The user then gets a
numbered list of completion candidates whose end4 This is especially true for Japanese, a moraic language in which
every mora ends with a vowel that can be lengthened. In fact, speakers
typically use filled pauses to gain time to recall a word or to wait for alistener to help with word choice.
5 This form of expression is very natural in Japanese.

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Forward Speech Completion(1) Uttering “maikeru–.”[Entering the phrase “maikeru jakuson” (“Michael Jackson”)
when its last part (“jakuson”) is uncertain.](3) Uttering “No. 2.”(2) A pop-up window containing
completion candidates appears.

(4) The second candidate ishighlighted and bounces.

(5) The selected candidate “maikeru jakuson”
is determined as the recognition result.

Figure 1. Screen snapshots of forward speech completion.
Backward Speech Completion[Entering the phrase “maikeru jakuson” (“Michael Jackson”)
when its first part (“maikeru”) is uncertain.](1) Uttering “nantoka–.”(3) Uttering “jakuson.”(wildcard keyword)(2) A pop-up window with colorful flying
decorations appears.

(5) Uttering “No. 1.”(4) A window containing completion
candidates appears.

(6) The first candidate “maikeru jakuson”
is determined as the recognition result.

Figure 2. Screen snapshots of backward speech completion.
Music Playback[Playing back a musical piece of the artist “maikeru jakuson” (“Michael Jackson”)
whose name is determined by the speech-completion interface (Figures 1 and 2).]

(1) Continued from
Figure 1 (5) or 2 (6).

(3) Uttering“No. 1.”(2) A pop-up window containing a list of musical pieces appears.

(4) The first musical piece is highlighted and played back.

Figure 3. Screen snapshots of music playback.
ings acoustically resemble the uttered last part. Completion candidates are generated by replacing the wildcard keyword (filling in the first part) as if a wildcard
search was done.
The user can see other candidates by uttering the turningthe-page phrases, “next candidates” and “previous candidates,” displayed whenever there are too many candidates
to fit onto the screen. If all the candidates are inappropriate or the user wants to enter another name, the user cansimply ignore the displayed candidates and proceed with
the next utterance. When the user selects one of the can-didates by saying (reading out) either its number, the restof the name, or the entire name, that name is highlighted
and used for the music playback (Figure 3).
2.2. Implementation
Figure 4 shows a block diagram of the method for implementing the speech-completion interface: the two mainprocesses are the filled-pause detector (Section 2.2.1) andspeech recognizer (Section 2.2.2). All the names ofartists, musical pieces, and the corresponding sound files

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Endpoint detector

Audio signal input(Utterance detector)

Speaker B: How about Michael Jackson?

Filled-pause detector Filled-pause
periodFeature extractor
Jukebox player

Speech recognizer
capable of listing
completion candidates
Recognition result
Completion candidates
Recognition result
Interface manager

Figure 4.
Method for implementing the speechcompletion interface.
are stored on an SQL (Structured Query Language) database server. Each name of the artists and their pieces isalso registered as a single word in the system vocabularyof the speech recognizer. Note that we cannot convert anuttered fragment of a vocabulary word into text by using
an up-to-date HMM-based speech recognizer 6 because
the recognizer only accepts a combination of vocabulary
words: it is therefore necessary to extend the speech recognizer to deal with word fragments.
2.2.1. Filled-pause detector
To detect filled pauses in real time, we use a robust filledpause detection method [3]. This is a bottom-up methodthat can detect a lengthened vowel in any word througha sophisticated signal-processing technique. It determines
the beginning and end of each filled pause by finding two
acoustical features of filled pauses — small fundamental
frequency (voice pitch) transitions and small spectral envelope deformations.
2.2.2. Speech recognizer capable of listing completion
candidates
We extended a typical speech recognizer to provide a listof completion candidates whenever a filled pause was detected [4, 5]. Because single phonemes cannot be recognized accurately enough, up-to-date speech recognizers
do not determine a word’s phoneme sequence phonemeby phoneme. Instead, they choose the maximum likelihood (ML) hypothesis while pursuing multiple hypotheses on a vocabulary tree where all vocabulary words (i.e.,names of artists and musical pieces) are stored. When the
beginning of a filled pause is detected, the recognizer determines which completion method is to be invoked (forward or backward) on the basis of whether the wildcard
keyword is the ML hypothesis at that moment.
In forward speech completion, completion candidates
are obtained by deriving from the vocabulary tree thosewords that share the prefix corresponding to each incomplete word hypothesis for the uttered fragment: the candidates are obtained by tracing from the top 15 hypotheses
to the leaves on the tree.
In backward speech completion, it is necessary to obtain completion candidates by recognizing a last-part fragment uttered after the wildcard keyword, which is not reg6 If this text conversion was possible, the problem we are solving
would be similar to text-based completion and much easier. However,there is no such thing as a universal speech (phonetic) typewriter.

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Speaker A: Let’s change the background music.
Speaker A: Uhm..., okay. I like his hit song from 1991.
Speaker B: Yeah, the title is “Black or White.”
Speaker A: Uhm..., Black or White. (with a high pitch)
The system then plays the song “Black or White.”

Figure 5. An example of using the music playback systemwith the speech-spotter interface.
istered as a vocabulary word. We therefore introduced anentry node table that lists the roots (notes) from which the
speech recognizer starts searching. Just after the wildcard
keyword, every syllable in the middle of all the vocabulary words is temporarily added to the table. Then, after
the last-part fragment is uttered, the hypotheses that havereached leaves are considered completion candidates.
3. MUSIC PLAYBACK SYSTEM WITH THE
SPEECH-SPOTTER INTERFACEIn this system, a user can listen to background music bysaying its title or the artist’s name while talking to anotherperson, as illustrated in Figure 5. For this system to bepractical, it must be able to monitor human-human conversations without disturbing them and provide music playback only when asked for it. We think such on-demand
music playback assistance in human-human conversation
is useful and convenient because it does not require theuse of any input device other than a microphone.
It has been difficult, however, to achieve a practicalmeans of providing such assistance by using only microphone input. Previous approaches using only speech information detected keywords in speech signals by meansof word-spotting technology [6, 7]. These techniques,though, are poor at judging, without the context being restricted in advance, whether the detected keywords are intended to be command utterances (voice commands formusic-playback control) for a computer system or conversational utterances for a conversational partner. Although
there have been other spotting approaches which requiredthat an utterance intended for the system be preceded bya keyword, such as Computer, Casper, or Maxwell, thisrestricted the usual behavior of a user: the user was forced
to avoid use of the keyword in human-human conversation in front of the microphone. Other previous speechinterface systems have had to use other input devices suchas a button or a camera [8, 9]. In short, no previous
approach allowed a system to identify a command utterance in conversation without the context being restricted
or some other device being used.
We therefore developed the speech-spotter interface
which enables a user to request music playback only whendesired while talking to another person. This interface regards a user utterance as a command utterance only when
it is intentionally uttered with a high pitch just after afilled pause such as “er...” or “uh...”. In other words, acomputer system accepts this specially designed unnatu-

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ral utterance only and ignores other normal utterances inhuman-human conversation. For example, when a user
enters the title of a musical piece by saying “Er... (afilled pause), Black or White (an utterance with a highpitch)”, 7 the system plays back the corresponding soundfile. For this speech-spotter utterance, we use the unnaturalness of nonverbal speech information — in this case an
intentional filled pause and a subsequent high-pitch utterance — because this combination is not normally utteredin (Japanese) human-human conversation but neverthelesscan be easily uttered.
This interface provides three benefits:
1. In human-human conversation, speech-based assistance can immediately be used whenever needed.
2. A hands-free interface system with only a microphone
is achieved. A user is free regarding body movement
and can use the system even during a telephone conversation.
3. A user can feel free to use any words in conversation
with another person. The user does not have to carefully avoid saying anything that the system will accept
as input.
3.1. Search methods
Our music playback system supports the following searchmethods:• Specifying the musical-piece title
When the title of a musical piece is uttered, such as“Er..., Without You”, the system plays back the corresponding sound file. It also either shows the title on
the screen, has a speech synthesizer read out the title,or both.
• Specifying the artist’s name
When the name of an artist is uttered, such as “Uhm...,Mariah Carey”, the system shows a numbered list ofmusical-piece titles for that artist on the screen or has
the speech synthesizer read out the list. After the user
selects a musical piece by saying the speech-spotter
utterance of either the title or its number, the system
plays back the piece. It also highlights the selected
title or reads out the title.
The system allows the user to say speech-spotter utterances at any time by overlapping and interrupting the
speech synthesis or music playback. The user, for example, can stop the music playback by saying “Uh..., stop”,
or change the current piece by saying another title.
This system is useful not only when a user would liketo enjoy background music, but also when a user would
like to talk about music in telephone conversations while
listening to it; note that the system does not disturb such
conversations. In particular, this is very effective for people who like to listen to music in everyday life because it
makes it much easier for them to share background music
and discuss it during playback on the telephone. The system can also be used to change background music in an
actual room where people are talking.
7 In this paper, overlining indicates that the pitch of the underlined
words is intentionally raised by a user.

Audio signal input

Filled-pause period

Filled-pause detector
Feature extractor

F0 estimator

Endpoint detector(Utterance detector)

Maximum likeliBeginning andhood hypothesis
end points
Speech recognizer

MFCC

Pitch (F0)(Modified CSRC toolkit)

Recognition result
Utterance classifier(Pitch classifier)

Speech-spotter utterance
Jukebox player

Figure 6. Method for implementing the speech-spotter
interface.
3.2. Implementation
Figure 6 shows a block diagram of the method for implementing the speech-spotter interface. The four mainprocesses are the filled-pause detector (Section 2.2.1),
endpoint detector (Section 3.2.1), speech recognizer(Section 3.2.2), and utterance classifier (Section 3.2.3).
Like the implementation of the speech-completion interface, all the names are stored on the SQL database serverand each name is registered as a single word in the system
vocabulary.
Speech-spotter utterances can be detected through thefollowing four steps:
1. Each filled pause is detected by the filled-pause detector described in Section 2.2.1.
2. When triggered by a detected filled pause, the endpoint detector determines the beginning of an utterance.
3. While the content of the utterance is being recognizedby the speech recognizer, the end of the utterance is
automatically determined by the endpoint detector.
4. The average pitch of the utterance whose beginningand end points were determined above is judged to behigh or normal by the utterance classifier.
3.2.1. Determining the beginning of an utterance (endpoint detector)
Whenever a filled pause is detected, the beginning of thesubsequent utterance is determined as being 130 ms before the end of the filled pause — i.e., as being in the
middle of the filled pause. Every lengthened vowel (andsubsequent consonant if necessary) should be inserted at
the beginning of the grammar.
3.2.2. Determining the end of an utterance (endpoint detector and speech recognizer)
After the HMM-based speech recognizer starts decoding
the current utterance, the endpoint detector checks theML hypothesis (intermediate speech-recognition result)for every frame. In the frame-synchronous Viterbi beam
search, if the ML hypothesis stays at a unique node that is
not shared by other words in a tree dictionary or a silence
node that corresponds to the silence at the end of a sentence, its frame is considered the end of the utterance andthe speech recognizer stops decoding [10].

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3.2.3. Judging the voice pitch (utterance classifier)

5. CONCLUSION

On the basis of a speaker-independent pitch-classification
method using a threshold relative to the base fundamental
frequency (base F0) [11], the utterance classifier filters
out normal-pitch utterances to obtain high-pitch speechspotter utterances. The base F0 is a unique pitch reference
that corresponds to the pitch of the speaker’s natural voice
and can be estimated by averaging the voice pitch during
a filled pause. If the relative pitch value of an utterance,
which is calculated by subtracting the base F0 from thepitch averaged over the utterance, is higher than a threshold, the utterance is judged to be a speech-spotter utterance.
4. EXPERIMENTAL RESULTS
We describe the results from evaluating the effectivenessof the system with the speech-completion interface andthe system with the speech-spotter interface.
4.1. Evaluation of the speech-completion interface
We tested the system with 45 Japanese subjects (24 male,
21 female). To evaluate whether the subjects preferred touse speech completion after gaining a good command ofit, we measured the usage frequencies of speech completion under two conditions: (a) when a subject input a set ofname entries from a list by freely using speech completionaccording to personal preference, and (b) when a subject
had to recall and input vaguely remembered entries.
We found that the average usage frequency of speechcompletion was 74.2% and 80.4%, respectively, for conditions (a) and (b). These results showed that the subjects preferred to use the speech-completion function evenwhen they could choose not to use it. Subjective questionnaire results indicated that the speech-completion interface was helpful and easy to use, and made it easy torecall and input uncertain phrases.
4.2. Evaluation of the speech-spotter interface
We analyzed the detection performance for speech-spotter
utterances on a 40-minute corpus consisting of both normal utterances of sentences naturally spoken with spontaneous filled pauses and speech-spotter utterances of 218
names of musicians and songs by 12 Japanese subjects.
We found that the recall and precision rates for detecting speech-spotter utterances were 0.78 and 0.77, respectively. In our experience with the music playback system, users without any training were able to start playback of background music and change it while talking on
cellular or normal phones. They felt that the practical performance was much higher than the above rates indicate
because visual feedback enabled the users to know how
long a vowel should be lengthened during a filled pause.
Although melody ringers (cellular phone ring-tones) are
widely used, our users had no previous experience of listening to music in the midst of telephone conversation,
and appreciated its novelty and usefulness.

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We have described two speech-recognition interfaces suitable for MIR, speech completion and speech spotter, anddemonstrated their usefulness in two different music jukebox systems. The music-retrieval system with the speechcompletion interface enables a user to listen to a musicalpiece even if part of its name cannot be recalled. The music playback system with the speech-spotter interface enables users to share music playback on the telephone as if
they were talking in the same room with background music. As far as we know, this is the first system that people
can use to obtain speech-based music information assistance in the midst of a telephone conversation.
We believe that practical speech-recognition interfaces
for MIR cannot be achieved by simply applying the current automatic speech recognition to MIR: retrieval of musical pieces just by uttering entire titles or artist names
is not sufficient. The two interfaces described in this paper can be considered an important first step toward building the ultimate speech-capable MIR interface. It will become more and more important to explore various speechrecognition interfaces for MIR as well as other traditional
MIR interfaces.
In the future, we plan to build a unified system wherea user can use, from a single microphone input, both of
the systems described in this paper as well as a query-byhumming (QBH) system to leverage the potential affinity
between speech-recognition interfaces and QBH systems.
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