Abstract:
Techniques have been developed to facilitate the capture performances on handheld or other portable computing devices and, in some cases, the pitch-correction and mixing of such vocal performances with backing tracks for audible rendering on such devices. Captivating visual animations and/or facilities for listener comment and ranking are provided in association with an audible rendering of a performance, e.g., a vocal performance captured and pitch-corrected at another similarly configured mobile device and mixed with backing instrumentals and/or vocals. Geocoding of captured vocal performances and/or listener feedback may facilitate animations or display artifacts in ways that are suggestive of a performance or endorsement emanating from a particular geographic locale on a user manipulable globe. In this way, implementations of the described functionality can transform otherwise mundane mobile devices into social instruments that foster a unique sense of global connectivity and community.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims the benefit of U.S. Provisional Application Nos. 61/286,749, filed Dec. 15, 2009, which is incorporated herein by reference. 
     In addition, the present application is related to the following co-pending applications each filed on even date herewith: (1) U.S. application Ser. No. 12/876,131, entitled “CONTINUOUS PITCH-CORRECTED VOCAL CAPTURE DEVICE COOPERATIVE WITH CONTENT SERVER FOR BACKING TRACK MIX” and naming and Salazar, Fiebrink, Wang, Ljungström, Smith and Cook as inventors and (2) U.S. application Ser. No. 12/876,132, entitled “CONTINUOUS SCORE-CODED PITCH CORRECTION” and naming and Salazar, Fiebrink, Wang, Ljungström, Smith and Cook as inventors. Each of the aforementioned co-pending applications is incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to user interface techniques for portable computing devices that audibly render performances and, in particular, to techniques suitable for user community interaction with captured and pitch-corrected vocal performances. 
     2. Description of the Related Art 
     The installed base of mobile phones and other portable computing devices grows in sheer number and computational power each day. Hyper-ubiquitous and deeply entrenched in the lifestyles of people around the world, they transcend nearly every cultural and economic barrier. Computationally, the mobile phones of today offer speed and storage capabilities comparable to desktop computers from less than ten years ago, rendering them surprisingly suitable for real-time sound synthesis and other musical applications. Partly as a result, some modern mobile phones, such as the iPhone™ handheld digital device, available from Apple Inc., support audio and video playback quite capably. 
     Like traditional acoustic instruments, mobile phones are intimate sound producing devices. However, by comparison to most traditional instruments, they are somewhat limited in acoustic bandwidth and power. Nonetheless, despite these disadvantages, mobile phones do have the advantages of ubiquity, strength in numbers, and ultramobility, making it feasible to (at least in theory) bring together artists for jam sessions, rehearsals, and even performance almost anywhere, anytime. The field of mobile music has been explored in several developing bodies of research. See generally, G. Wang,  Designing Smule&#39;s iPhone Ocarina , presented at the 2009  on New Interfaces for Musical Expression , Pittsburgh (June 2009). Recent experience with applications such as the Smule Ocarina™ and Smule Leaf Trombone: World Stage™ has shown that advanced digital acoustic techniques may be delivered in ways that provide a compelling user experience. 
     As digital acoustic researchers seek to transition their innovations to commercial applications deployable to modern handheld devices such as the iPhone® handheld and other platforms operable within the real-world constraints imposed by processor, memory and other limited computational resources thereof and/or within communications bandwidth and transmission latency constraints typical of wireless networks, significant practical challenges present. While some, though not all of these challenges involve signal processing techniques, encoding forms and data-transfer-bandwidth sensitive allocation of functionality throughout a distributed network of devices, to achieve a compelling user experience, improved user interface techniques are also needed. 
     SUMMARY 
     Techniques have been developed to facilitate the capture performances on handheld or other portable computing devices and, in some cases, the pitch-correction and mixing of vocal performances with backing tracks for audible rendering on such devices. Captivating visual animations and/or facilities for listener comment and ranking are provided in association with an audible rendering of a performance, e.g., a vocal performance captured and pitch-corrected at another similarly configured mobile device and mixed with backing instrumentals and/or vocals. Geocoding of captured vocal performances and/or listener feedback may facilitate animations or display artifacts in ways that are suggestive of a performance or endorsement emanating from a particular geographic locale on a user manipulable globe. In this way, implementations of the described functionality can transform otherwise mundane mobile devices into social instruments that foster a unique sense of global connectivity and community. 
     In some exploitations of the developed techniques, vocal performances may be captured and continuously pitch-corrected for mixing and rendering with backing tracks in ways that create compelling user experiences. In some cases, the vocal performances of individual users are captured on mobile devices in the context of a karaoke-style presentation of lyrics in correspondence with audible renderings of a backing track. Such performances can be pitch corrected in real-time at the mobile device (or more generally, at a portable computing device such as a mobile phone, personal digital assistant, laptop computer, notebook computer, pad-type computer or netbook) in accord with pitch correction settings. In some cases, such pitch correction settings code a particular key or scale for the vocal performance or for portions thereof. In some cases, pitch correction settings include a score-coded melody sequence of note targets supplied with, or for association with, the lyrics and/or backing track. 
     In these ways, user performances (typically those of amateur vocalists) can be significantly improved in tonal quality and the user can be provided with immediate and encouraging feedback. Typically, feedback includes the pitch-corrected vocals themselves and visual reinforcement (during vocal capture) when the user/vocalist is “hitting” the (or a) correct note. In some cases, pitch correction settings are characteristic of a particular artist or of a particular vocal performance of the lyrics in correspondence with the backing track. In this way, tonal characteristics of vocals captured from a user&#39;s vocal performance may altered with effects popularized by artists such as Cher, T-Pain and others. In some cases, the effects include pitch-corrections commonly associated with Auto-Tune® audio processing technology available from Antares Audio Technologies. In some cases, alternative audio processing techniques may be employed. 
     In some embodiments in accordance with the present invention, a method includes using a portable computing device for audible rendering of captured vocal performances, the portable computing device having a display, an audio transducer interface and a data communications interface. In particular, the method includes retrieving, via the data communications interface, both (i) an encoding of a first pitch-corrected vocal performance and (ii) an associated first geocode. The retrieved first pitch-corrected vocal performance encoding is audibly rendered at the portable computing device in association with a visual display animation suggestive of the first pitch-corrected vocal performance emanating from a particular location on a globe, wherein the particular location corresponds to the first geocode, the first geocode coding a remote device location at which the first vocal performance was originally captured and pitch corrected. 
     In some embodiments, the method further includes retrieving, via the data communications interface, additional geocoded metadata indicative of listener feedback on the first pitch-corrected vocal performance; and including with the visual display animation further visual indications of the listener feedback, the further visual indications positioned on the globe of the visual display animation to suggest, consistent with the geocoded metadata, a geographic location from which the corresponding listener feedback was transmitted. 
     In some cases, the retrieved first pitch-corrected vocal performance is mixed with a backing track. In some embodiments, the method further includes retrieving via the data communications interface lyrics and timing information corresponding to the backing track; audibly rendering the backing track and, in accord with the retrieved timing information, concurrently presenting the retrieved lyrics on the display; at the portable computing device, capturing and pitch correcting a second vocal performance; and transmitting to a remote server via the communications interface both an audio encoding of the second pitch-corrected vocal performance and an associated second geocode indicative of geographic location of the portable computing device. In some embodiments, the method further includes retrieving the backing track via the data communications interface. In some embodiments, the method further includes mixing the pitch-corrected vocal performance with the backing track at the portable computing device. 
     In some embodiments, the method further includes at the portable computing device, capturing, geocoding and transmitting listener comment on the first pitch-corrected vocal performance for inclusion as metadata in association with subsequent supply and rendering thereof. 
     In some cases, the portable computing device is a mobile phone. In some cases, the portable computing device is a personal digital assistant. In some cases, the portable computing device is a laptop computer, notebook computer, pad-type device or netbook. 
     In some embodiments in accordance with the present invention, a method includes using a portable computing device for audible rendering of a remotely captured performance, the portable computing device having a display, an audio transducer interface and a data communications interface. In particular, the method includes retrieving, via the data communications interface, (i) an encoding of the remotely captured performance, (ii) an associated first geocode and (iii) additional geocoded metadata encoding feedback from respective prior audible renderings of the remotely captured performance. The retrieved remotely captured performance encoding is audibly rendered at the portable computing device in association with both: (i) a visual display animation suggestive of the performance emanating from a particular location on a globe, wherein the particular location corresponds to the first geocode associated with a remote device location at which the performance was originally captured and (ii) further visual indications positioned on the globe of the visual display animation to suggest, consistent with the geocoded metadata, respective geographic locations from which the corresponding listener feedback was transmitted. 
     In some embodiments, the method further includes: at the portable computing device, capturing, geocoding and transmitting further listener feedback on the audible rendering the retrieved remotely captured performance for inclusion as additional metadata in association with subsequent supply and rendering thereof. 
     In some cases, the remotely captured performance is a pitch-corrected vocal performance. In some cases, the retrieved remotely captured performance encoding includes an audio encoding. 
     In some embodiments in accordance with the present invention, a portable computing device includes a display, a microphone interface, an audio transducer interface and a data communications interface, as well a data communications code, playback code and user interface code each executable on the portable computing device. The data communications code is executable to retrieve from a remote server via the data communications interface both (i) an encoding of a first pitch-corrected vocal performance and (ii) an associated first geocode indicative of a remote device location at which first pitch-corrected vocal performance was originally captured and pitch corrected. The playback code is executable to audibly render the first pitch-corrected vocal performance. The user interface code is executable to, in association with the audible rendering, present on the display a visual display animation suggestive of the first pitch-corrected vocal performance emanating from a particular location on a globe, the particular location corresponding to the first geocode. 
     In some embodiments, the data communications code is further executable to retrieve via the data communications interface additional geocoded metadata indicative of listener feedback on the first pitch-corrected vocal performance; and the user interface code is further executable to include with the visual display animation further visual indications of the listener feedback, the further visual indications positioned on the globe of the visual display animation to suggest, consistent with the geocoded metadata, geographic locations from which the corresponding listener feedback was transmitted. 
     In some embodiments, the data communications code is further executable to retrieve lyrics and timing information corresponding to a backing track with which the retrieved encoding of the first pitch-corrected vocal performance is mixed. The playback code is further executable to audibly render the backing track and, in accord with the retrieved timing information, to concurrently present the retrieved lyrics on the display. The portable communication device further includes pitch correction code executable at the portable computing device to pitch correct a second vocal performance captured from the microphone interface. Finally, the data communications code is further executable to transmit to the remote server via the communications interface both an audio encoding of the second pitch-corrected vocal performance and an associated second geocode indicative of geographic location of the portable computing device. 
     In some embodiments in accordance with the present invention, a computer program product is encoded in one or more media, the computer program product includes instructions executable on a processor of the portable computing device to cause the portable computing device to: retrieve via the data communications interface, both (i) an encoding of a first pitch-corrected vocal performance and (ii) an associated first geocode indicative of a remote device location at which the first pitch-corrected vocal performance was originally captured and pitch corrected; and audibly render the retrieved first pitch-corrected vocal performance encoding at the portable computing device in association with a visual display animation suggestive of the first pitch-corrected vocal performance emanating from a particular location on a globe, wherein the particular location corresponds to the first geocode. 
     In some embodiments the instructions are executable on the processor of the portable computing device to further cause the portable computing device to retrieve via the data communications interface, additional geocoded metadata indicative of listener feedback on the first pitch-corrected vocal performance; and include with the visual display animation further visual indications of the listener feedback, the further visual indications positioned on the globe of the visual display animation to suggest, consistent with the geocoded metadata, a geographic location from which the corresponding listener feedback was transmitted. 
     In some embodiments, the instructions are executable on the processor of the portable computing device to further cause the portable computing device to retrieve lyrics and timing information corresponding to a backing track with which the retrieved encoding of the first pitch-corrected vocal performance is mixed; audibly render the backing track and, in accord with the retrieved timing information, concurrently present the retrieved lyrics on the display; capture and pitch correct a second vocal performance; and transmit to the remote server via the communications interface, both an audio encoding of the second pitch-corrected vocal performance and an associated second geocode indicative of geographic location of the portable computing device. 
     These and other embodiments in accordance with the present invention(s) will be understood with reference to the description and appended claims which follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example and not limitation with reference to the accompanying figures, in which like references generally indicate similar elements or features. 
         FIG. 1  depicts information flows amongst illustrative mobile phone-type portable computing devices and a content server in accordance with some embodiments of the present invention. 
         FIG. 2  is a functional block diagram of hardware and software components executable at an illustrative mobile phone-type portable computing device in accordance with some embodiments of the present invention. 
         FIG. 3  illustrates a flow diagram illustrating, for a captured vocal performance, real-time continuous pitch-correction based on score-coded pitch correction settings in accordance with some embodiments of the present invention. 
         FIG. 4  illustrates features of a mobile device that may serve as a platform for execution of software implementations in accordance with some embodiments of the present invention. 
         FIG. 5  is a network diagram that illustrates cooperation of exemplary devices in accordance with some embodiments of the present invention. 
     
    
    
     Skilled artisans will appreciate that elements or features in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions or prominence of some of the illustrated elements or features may be exaggerated relative to other elements or features in an effort to help to improve understanding of embodiments of the present invention. 
     DESCRIPTION 
     Techniques have been developed to facilitate (1) the capture and pitch correction of vocal performances on handheld or other portable computing devices and (2) the mixing of such pitch-corrected vocal performances with backing tracks for audible rendering on targets that include such portable computing devices and as well as desktops, workstations, gaming stations and even telephony targets. Implementations of the described techniques employ signal processing techniques and allocations of system functionality that are suitable given the generally limited capabilities of such handheld or portable computing devices and that facilitate efficient encoding and communication of the pitch-corrected vocal performances (or precursors or derivatives thereof) via wireless and/or wired bandwidth-limited networks for rendering on portable computing devices or other targets. 
     In some cases, the developed techniques build upon vocal performance capture with continuous, real-time pitch detection and correction and upon encoding/transmission of such pitch-corrected vocals to a content server where, in some embodiments, they may be mixed with backing tracks (e.g., instrumentals, vocals, etc.) and encoded for delivery to a device at which they will be audibly rendered. In some cases, mixing of pitch-corrected vocals with backing tracks may be performed at the rendering target itself. Typically, first and second encodings are respective versions (often of differing quality or fidelity) of the same underlying audio source material, although in some cases or situations, different source material with equivalent timing may be employed. 
     Use of first and second encodings of such a backing track (e.g., one at the handheld or other portable computing device at which vocals are captured, and one at the content server) allows the respective encodings to be adapted to data transfer bandwidth constraints or to needs at the particular device/platform at which they are employed. For example, in some embodiments, a first encoding of the backing track audibly rendered at a handheld or other portable computing device as an audio backdrop to vocal capture may be of lesser quality or fidelity than a second encoding of that same backing track used at the content server to prepare the mixed performance for audible rendering. In this way, high quality mixed audio content may be provided while limiting data bandwidth requirements to a handheld device used for capture and pitch correction of a vocal performance. Notwithstanding the foregoing, backing track encodings employed at the portable computing device may, in some cases, be of equivalent or even better quality/fidelity those at the content server. For example, in embodiments or situations in which a suitable encoding of the backing track already exists at the mobile phone (or other portable computing device), such as from a music library resident thereon or based on prior download from the content server, download data bandwidth requirements may be quite low. Lyrics, timing information and applicable pitch correction settings may be retrieved for association with the existing backing track using any of a variety of identifiers ascertainable, e.g., from audio metadata, track title, an associated thumbnail or even fingerprinting techniques applied to the audio, if desired. 
     Pitch detection and correction of a user&#39;s vocal performance are performed continuously and in real-time with respect to the audible rendering of the backing track at the mobile phone (or other portable computing device). In this way, the pitch-corrected vocal performance may be mixed with the audible rendering to overlay instrumentals and/or vocals of the backing track. In some multi-technique implementations, pitch detection builds on time-domain pitch correction techniques that employ average magnitude difference function (AMDF) or autocorrelation-based techniques together with zero-crossing and/or peak picking techniques to identify differences between pitch of a captured vocal signal and score-coded target pitches. Based on detected differences, pitch correction based on pitch synchronous overlapped add (PSOLA) and/or linear predictive coding (LPC) techniques allow captured vocals to be pitch-corrected in real-time to “correct” notes in accord with pitch correction settings that include score-coded note targets. Alternatively, or in addition, pitch correction settings may select a particular scale or key for the vocal performance or particular portions thereof. Alternatively, or in addition, pitch correction settings may be selected to distort the captured vocal performance in accord with a desired effect, such as with pitch correction effects popularized by a particular musical performance or particular artist. In some embodiments, pitch correction may be based on techniques that computationally simplify autocorrelation calculations as applied to a variable window of samples from a captured vocal signal, such as with plug-in implementations of Auto-Tune® technology popularized by, and available from, Antares Audio Technologies. Frequency domain techniques, such as FFT peak picking for pitch detection and phase vocoding for pitch shifting, may be used in some implementations. 
     In general, “correct” notes are those notes that are consistent with a specified key or scale or which, in some embodiments, correspond to a score-coded melody (or harmony) expected in accord with a particular point in the performance. That said, in a capella modes without an operant score (or that allow a user to, during vocal capture, dynamically vary pitch correction settings of an existing score) may be provided in some implementations to facilitate ad-libbing. For example, user interface gestures captured at the mobile phone (or other portable computing device) may, for particular lyrics, allow the user to (i) switch off (and on) use of score-coded note targets, (ii) dynamically switch back and forth between melody and harmony note sets as operant pitch correction settings and/or (iii) selectively fall back (at gesture selected points in the vocal capture) to settings that cause sounded pitches to be corrected solely to nearest notes of a particular key or scale (e.g., C major, C minor, E flat major, etc.) In short, user interface gesture capture and dynamically variable pitch correction settings can provide a Freestyle mode for advanced users. 
     Based on the compelling and transformative nature of the pitch-corrected vocals, user/vocalists typically overcome an otherwise natural shyness or angst associated with sharing their vocal performances. Instead, even mere amateurs are encouraged to share with friends and family or to collaborate and contribute vocal performances as part of an affinity group. In some implementations, these interactions are facilitated through social network- and/or eMail-mediated sharing of performances and invitations to join in a group performance. Using uploaded vocals captured at clients such as the aforementioned portable computing devices, a content server (or service) can mediate such affinity groups by manipulating and mixing the uploaded vocal performances of multiple contributing vocalists. Depending on the goals and implementation of a particular system, uploads may include pitch-corrected vocal performances, dry (i.e., uncorrected) vocals, and/or control tracks of user key and/or pitch correction selections, etc. 
     Karaoke-Style Vocal Performance Capture 
     Although embodiments of the present invention are not limited thereto, mobile phone-hosted, pitch-corrected, karaoke-style, vocal capture provides a useful descriptive context. For example, in some embodiments such as illustrated in  FIG. 1 , an iPhone™ handheld available from Apple Inc. (or more generally, handheld  101 ) hosts software that executes in coordination with a content server to provide vocal capture and continuous real-time, score-coded pitch correction of the captured vocals. As is typical of karaoke-style applications (such as the “I am T-Pain” application for iPhone available from SonicMule, Inc.), a backing track of instrumentals and/or vocals can be audibly rendered for a user/vocalist to sing against. In such cases, lyrics may be displayed in correspondence with the audible rendering so as to facilitate a karaoke-style vocal performance by a user. In some cases or situations, backing audio may be rendered from a local store such as from content of an iTunes™ library resident on the handheld. 
     User vocals are captured at the handheld, pitch-corrected continuously and in real-time (again at the handheld) and audibly rendered (mixed with the backing track) to provide the user with an improved tonal quality rendition of his/her own vocal performance. Pitch correction is typically based on score-coded melody or harmony note sets or cues, which provide continuous pitch-correction with performance synchronized sequences of target notes in a current key or scale. In some cases, pitch correction settings may be characteristic of a particular artist such as the artist that performed vocals associated with the particular backing track. 
     In the illustrated embodiment, backing audio (here, one or more instrumental/vocal tracks), lyrics and timing information and pitch/harmony cues are all supplied (or demand updated) from one or more content servers or hosted service platforms (here, content server  110 ). For a given song and performance, such as “I′m in Luv (with a . . . )”, several versions of the background track may be stored, e.g., on the content server. For example, in some implementations or deployments, versions may include:
         uncompressed stereo wav format backing track,   uncompressed mono wav format backing track and   compressed mono m4a format backing track.       

     In addition, lyrics, melody and harmony track note sets and related timing and control information may be encapsulated as a score coded in an appropriate container or object (e.g., in a Musical Instrument Digital Interface, MIDI, or Java Script Object Notation, json, type format) for supply together with the backing track(s). Using such information, handheld  101  may display lyrics and even visual cues related to target notes, harmonies and currently detected vocal pitch in correspondence with an audible performance of the backing track(s) so as to facilitate a karaoke-style vocal performance by a user. 
     Thus, if an aspiring vocalist selects on the handheld device “I&#39;m in Luv (with a . . . )” as originally popularized by the artist T-Pain, iminluv.json and iminluv.m4a may be downloaded from the content server (if not already available or cached based on prior download) and, in turn, used to provide background music, synchronized lyrics and, in some situations or embodiments, score-coded note tracks for continuous, real-time pitch-correction shifts while the user sings. Optionally, at least for certain embodiments or genres, harmony note tracks may be score coded for harmony shifts to captured vocals. Typically, a captured pitch-corrected (or possibly harmonized) vocal performance is saved locally on the handheld device as one or more wav files and is subsequently compressed (e.g., using lossless Apple Lossless Encoder, ALE, or lossy Advanced Audio Coding, AAC, or vorbis codec) and encoded for upload to the content server as an MPEG-4 audio, m4a, or ogg container file. MPEG-4 is an international standard for the coded representation and transmission of digital multimedia content for the Internet, mobile networks and advanced broadcast applications. OGG is an open standard container format often used in association with the vorbis audio format specification and codec for lossy audio compression. Other suitable codecs, compression techniques, coding formats and/or containers may be employed if desired. 
     Depending on the implementation, encodings of dry vocal and/or pitch-corrected vocals may be uploaded to the content server. In general, such vocals (encoded, e.g., as wav, m4a, ogg/vorbis content or otherwise) whether already pitch-corrected or pitch-corrected at the content server can then be mixed (e.g., with backing audio) to produce files or streams of quality or coding characteristics selected accord with capabilities or limitations a particular target or network. For example, pitch-corrected vocals can be mixed with both the stereo and mono way files to produce streams of differing quality. For example, a high quality stereo version can be produced for web playback and a lower quality mono version for streaming to devices such as the handheld device itself. 
     Pitch Correction, Generally 
     In some cases, it may be desirable to pitch correct the captured vocal performance using a vocoder or similar technique at the handheld device. For example, in some embodiments, an Antares Auto-Tune® implementation is provided at the handheld device and may be activated anytime vocal capture is operating with a hot microphone. In such case, the vocal capture application takes the audio input from the microphone and runs it (in real time) through the Auto-Tune® library, saving the resulting pitch-corrected vocal performance to local storage (for upload to the content server). Typically, the handheld application locally mixes the pitch-corrected vocal performance with the background instrumentals and/or background vocals (more generally, a backing track) for real time audible rendering. 
     In general, the previously described json format file includes lyrics and timing information as well as pitch correction settings such as the pitches to which a vocal performance should be tuned and/or the level of pitch correction desired. Pitch correction settings may be specified on a global basis for an entire song (for example, pitch correct to C major scale), or can be synchronized and used in conjunction with individual lyrics timings so that the precise pitch of particular notes/syllables can be specified. In some embodiments, pitch correction can detect whether (and how much) a given vocal performance is on/off key and apply different levels of assistance as needed to improve the performance. In some embodiments, pitch correction can be used to provide vocal effects in accord with a particular or popular performance of the selected track or in accord with characteristic effects employed by a particular artist. 
     As will be appreciated by persons of ordinary skill in the art having benefit of the present description, pitch-detection and correction techniques may be employed both for correction of a captured vocal signal to a target pitch or note as well as for generation of harmonies as pitch-shifted variants of the captured vocal signal.  FIGS. 2 and 3  illustrate basic signal processing flows ( 250 ,  350 ) in accord with certain illustrative implementations suitable for an iPhone™ handheld, e.g., that illustrated as mobile device  201 , to generate the pitch-corrected (and, in the case of  FIG. 3 , optionally harmonized vocals) supplied for audible rendering by (or at) one or more target devices. 
     As will also be appreciated by persons of ordinary skill in the art, pitch-detection and pitch-correction have a rich technological history in the music and voice coding arts. Indeed, a wide variety of feature picking, time-domain and even frequency domain techniques have been employed in the art and may be employed in some embodiments in accord with the present invention. The present description does not seek to exhaustively inventory the wide variety of signal processing techniques that may be suitable in various design or implementations in accord with the present description; rather, we summarize certain techniques that have proved workable in implementations (such as mobile device applications) that contend with CPU-limited computational platforms. Based on the description herein, persons of ordinary skill in the art will appreciate suitable allocations of signal processing techniques (sampling, filtering, decimation, etc.) and data representations to functional blocks (e.g., decoder(s)  252 , digital-to-analog (D/A) converter  251 , capture  253 , pitch correction  254  and encoder  255 ) of signal processing flows  250  illustrated in  FIG. 2 . Likewise, relative to the signal processing flows  350  and illustrative score coded note targets (including harmony note targets), persons of ordinary skill in the art will appreciate suitable allocations of signal processing techniques and data representations to functional blocks and signal processing constructs (e.g., decoder  350 , capture  351 , pitch correction  352 , mixers  353 ,  356 , and encoder  357 ) illustrated in  FIG. 3 . 
     Accordingly, in view of the above and without limitation, certain exemplary embodiments operate as follows:
         1) Get a buffer of audio data containing the sampled user vocals.   2) Downsample from a 44.1 kHz sample rate by low-pass filtering and decimation to 22 k (for use in pitch detection and correction of sampled vocals as a main voice, typically to score-coded melody note target) and to 11 k (for pitch detection and shifting of harmony variants of the sampled vocals).   3) Call a pitch detector (PitchDetector::CalculatePitch ( )), which first checks to see if the sampled audio signal is of sufficient amplitude and if that sampled audio isn&#39;t too noisy (excessive zero crossings) to proceed. If the sampled audio is acceptable, the CalculatePitch ( )method calculates an average magnitude difference function (AMDF) and executes logic to pick a peak that corresponds to an estimate of the pitch period. Additional processing refines that estimate. For example, in some embodiments parabolic interpolation of the peak and adjacent samples may be employed. In some embodiments and given adequate computational bandwidth, an additional AMDF may be run at a higher sample rate around the peak sample to get better frequency resolution.   4) Shift the main voice to a score-coded target pitch by using a pitch-synchronous overlap add (PSOLA) technique at a 22 kHz sample rate (for higher quality and overlap accuracy). The PSOLA implementation (Smola::PitchShiftVoice ( )) is called with data structures and Class variables that contain information (detected pitch, pitch target, etc.) needed to specify the desired correction. In general, target pitch is selected based on score-coded targets (which change frequently in correspondence with a melody note track) and in accord with current scale/mode settings. Scale/mode settings may be updated in the course of a particular vocal performance, but usually not too often based on score-coded information, or in an a capella or Freestyle mode based on user selections.
           PSOLA techniques facilitate resampling of a waveform to produce a pitch-shifted variant while reducing aperiodic affects of a splice and are well known in the art. PSOLA techniques build on the observation that it is possible to splice two periodic waveforms at similar points in their periodic oscillation (for example, at positive going zero crossings, ideally with roughly the same slope) with a much smoother result if you cross fade between them during a segment of overlap. For example, if we had a quasi periodic sequence like:   a b c d e d c b a b c d.1 e.2 d.2 c.1 b.1 a b.1 c.2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18   with samples {a, b, c, . . . } and indices 0, 1, 2, . . . (wherein the 0.1 symbology represents deviations from periodicity) and wanted to jump back or forward somewhere, we might pick the positive going c-d transitions at indices 2 and 10, and instead of just jumping, ramp:
 
(1*c+0*c),(d*⅞+(d.1)/8),(e* 6/8+(e.2)* 2/8) . . .
   until we reached (0*c+1*c.1) at index 10/18, having jumped forward a period (8 indices) but made the a periodicity less evident at the edit point. It is pitch synchronous because we do it at 8 samples, the closest period to what we can detect. Note that the cross-fade is a linear/triangular overlap-add, but (more generally) may employ complimentary cosine, 1-cosine, or other functions as desired.   
           5) Generate the harmony voices using a method that employs both PSOLA and linear predictive coding (LPC) techniques. The harmony notes are selected based on the current settings, which change often according to the score-coded harmony targets, or which in Freestyle can be changed by the user. These are target pitches as described above; however, given the generally larger pitch shift for harmonies, a different technique may be employed. The main voice (now at 22 k, or optionally 44 k) is pitch-corrected to target using PSOLA techniques such as described above. Pitch shifts to respective harmonies are likewise performed using PSOLA techniques. Then a linear predictive coding (LPC) is applied to each to generate a residue signal for each harmony. LPC is applied to the main un-pitch-corrected voice at 11 k (or optionally 22 k) in order to derive a spectral template to apply to the pitch-shifted residues. This tends to avoid the head-size modulation problem (chipmunk or munchkinification for upward shifts, or making people sound like Darth Vader for downward shifts).   6) Finally, the residues are mixed together and used to re-synthesize the respective pitch-shifted harmonies using the filter defined by LPC coefficients derived for the main un-pitch-corrected voice signal. The resulting mix of pitch-shifted harmonies are then mixed with the pitch-corrected main voice.   7) Resulting mix is upsampled back up to 44.1 k, mixed with the backing track (except in Freestyle mode) or an improved fidelity variant thereof buffered for handoff to audio subsystem for playback.
 
Function names, sampling rates and particular signal processing techniques applied are, of course, all matters of design choice and subject to adaptation for particular applications, implementations, deployments and audio sources.
 
Content Server for Mix with High Quality Backing Tracks
       

     Referring again to  FIG. 1 , once a user performance is captured at the handheld device, the captured vocal performance audio (typically pitch-corrected) is compressed using an audio codec (e.g., a vorbis codec) and included as an audio layer in an appropriate container object (e.g., in a file object in accord with the ogg container format) and uploaded to the content server  110 ,  210 . The content server then mixes ( 111 ,  211 ) the captured, pitch-corrected vocal performance encoding with the full instrumental (and/or background vocal) backing track (HQ version) to create high fidelity master audio. This master (not separately shown) may, in turn, be encoded using any techniques suitable for the target device(s) and/or the expected network transports. For example, in some embodiments, an AAC codec is used at various bit rates to produce compressed audio layers of M4A container files which are suitable for streaming back audio to the capturing handheld device (or to other remote devices) and for streaming/playback via the web. 
     Typically, the first and second encodings of backing tracks described herein are respective versions (often of differing quality or fidelity) of the same underlying audio source material. For example, in the illustration of  FIG. 1 , a first encoding (LQ MONO) of the backing track is of lesser quality/fidelity than a second encoding (HQ STEREO) thereof, but both are encodings, or derivative encodings, of the same performance by T-Pain of the song “I′m in Luv (with a . . . ” In some cases or situations, different source material with equivalent timing could be employed. 
     In general, use of first and second encodings of such a backing track (e.g., one at the handheld or other portable computing device at which vocals are captured, and one at the content server) allows the respective encodings to be adapted to data transfer bandwidth constraints or to needs at the particular device/platform at which they are employed. For example, in some embodiments, a first encoding of the backing track audibly rendered at a handheld or other portable computing device as an audio backdrop to vocal capture may be of lesser quality or fidelity than a second encoding of that same backing track used at the content server to prepare the mixed performance for audible rendering. In this way, high quality mixed audio content may be provided while limiting data bandwidth requirements to a handheld device such as a mobile phone used for capture and pitch correction of a vocal performance. Notwithstanding the foregoing, backing track encodings employed at the portable computing device may, in some cases, be of equivalent or even higher quality/fidelity than those at the content server. For example, in embodiments or situations in which a suitable encoding of the backing track already exists at the mobile phone (or other portable computing device), such as from a music library resident thereon or based on prior download from the content server, download data bandwidth requirements may be quite low. Lyrics, timing information and applicable pitch correction settings may be retrieved for association with the existing backing track using any of a variety of identifiers ascertainable, e.g., from audio metadata, track title, an associated thumbnail or even fingerprinting techniques applied to the audio, if desired. 
     In general, relative to capabilities of commonly deployed wireless networks, it can be desirable from an audio data bandwidth perspective to limit the uploaded data to that necessary to represent the vocal performance. In some cases, data streamed for playback may separate vocal tracks as well. In general, vocal and/or backing track audio exchange between the handheld device and content server may be adapted to the quality and capabilities of an available data connection. 
     Although the illustration of  FIG. 1  includes, for at least some targets at which the pitch-corrected vocal performance will be audibly rendered, mixing (at content server  110 ) with a high quality backing track (HQ), in some cases or for some targets, mixing of pitch-corrected vocals with a suitable backing track may be performed elsewhere, e.g., at the mixed performance rendering target itself. For example, just as locally-resident iTunes™ content may, in some embodiments or situations, be used at the vocal capture device as a first encoding of the backing track for audible rendering during capture, iTunes™ content at the eventual rendering target device may be mixed (at the rendering device) with a received pitch-corrected to produce the resulting mixed performance. It will be appreciated that, in embodiments or situations that allow respective locally-resident content to be used, at the vocal capture device, as a first encoding of the backing track and, at the rendering target, as a second encoding of the backing track, data transfer bandwidth requirements are advantageously reduced as audio data transfers need only encode the pitch-corrected vocal performance. Reductions in content licensing costs may also accrue in some situations. 
     As will be appreciated by persons of ordinary skill in the art based on the present description, the term “content server” is intended to have broad scope, encompassing not only a single physical server that hosts audio content and functionality described and illustrated herein, but also collections of server or service platforms that together host the audio content and functionality described. For example, in some embodiments, content server  110 ,  210  is implemented (at least in part) using hosted storage services such as popularized by platforms such as the Amazon Simple Storage Service (S3) platform. Functionality, such as mixing of backing audio with captured, pitch-corrected vocals, selection of appropriate source or target audio coding forms or containers and introduction of appropriately coded or transcoded audio into networks, etc. may itself by hosted on servers or service/compute platforms. 
     World Stage 
     Although much of the description herein has focused on vocal performance capture, pitch correction and use of respective first and second encodings of a backing track relative to capture and mix of a user&#39;s own vocal performances, it will be understood that facilities for audible rendering of remotely captured performances of others may be provided in some situations or embodiments. In such situations or embodiments, vocal performance capture occurs at another device and after a corresponding encoding of the captured (and typically pitch-corrected) vocal performance is received at a present device, it is audibly rendered in association with a visual display animation suggestive of the vocal performance emanating from a particular location on a globe.  FIG. 1  illustrates a snapshot of such a visual display animation at handheld  120 , which for purposes of the present illustration, will be understood as another instance of a programmed mobile phone (or other portable computing device) such as described and illustrated with reference to handheld device instances  101  and  201 , except that (as depicted with the snapshot) handheld  120  is operating in a play (or listener) mode, rather than the capture and pitch-correction mode described at length hereinabove. 
     When a user executes the handheld application and accesses this play (or listener) mode, a world stage is presented. More specifically, a network connection is made to content server  110  reporting the handheld&#39;s current network connectivity status and playback preference (e.g., random global, top loved, my performances, etc). Based on these parameters, content server  110  selects a performance (e.g., a pitch-corrected vocal performance such as may have been captured at handheld device instance  101  or  201  and transmits metadata associated therewith. In some implementations, the metadata includes a uniform resource locator (URL) that allows handheld  120  to retrieve the actual audio stream (high quality or low quality depending on the size of the pipe), as well as additional information such as geocoded (using GPS) location of the performance capture and attributes of other listeners who have loved, tagged or left comments for the particular performance. In some embodiments, listener feedback is itself geocoded. During playback, the user may tag the performance and leave his own feedback or comments for a subsequent listener and/or for the original vocal performer. Once a performance is tagged, a relationship may be established between the performer and the listener. In some cases, the listener may be allowed to filter for additional performances by the same performer and the server is also able to more intelligently provide “random” new performances for the user to listen to based on an evaluation of user preferences. 
     Although not specifically illustrated in the snapshot, it will be appreciated that geocoded listener feedback indications are, or may optionally be, presented on the globe (e.g., as stars or “thumbs up” or the like) at positions to suggest, consistent with the geocoded metadata, respective geographic locations from which the corresponding listener feedback was transmitted. It will be further appreciated that, in some embodiments, the visual display animation is interactive and subject to viewpoint manipulation in correspondence with user interface gestures captured at a touch screen display of handheld  120 . For example, in some embodiments, travel of a finger or stylus across a displayed image of the globe in the visual display animation causes the globe to rotate around an axis generally orthogonal to the direction of finger or stylus travel. Both the visual display animation suggestive of the vocal performance emanating from a particular location on a globe and the listener feedback indications are presented in such an interactive, rotating globe user interface presentation at positions consistent with their respective geotags. 
     An Exemplary Mobile Device 
       FIG. 4  illustrates features of a mobile device that may serve as a platform for execution of software implementations in accordance with some embodiments of the present invention. More specifically,  FIG. 4  is a block diagram of a mobile device  400  that is generally consistent with commercially-available versions of an iPhone™ mobile digital device. Although embodiments of the present invention are certainly not limited to iPhone deployments or applications (or even to iPhone-type devices), the iPhone device, together with its rich complement of sensors, multimedia facilities, application programmer interfaces and wireless application delivery model, provides a highly capable platform on which to deploy certain implementations. 
     Summarizing briefly, mobile device  400  includes a display  402  that can be sensitive to haptic and/or tactile contact with a user. Touch-sensitive display  402  can support multi-touch features, processing multiple simultaneous touch points, including processing data related to the pressure, degree and/or position of each touch point. Such processing facilitates gestures and interactions with multiple fingers, chording, and other interactions. Of course, other touch-sensitive display technologies can also be used, e.g., a display in which contact is made using a stylus or other pointing device. 
     Typically, mobile device  400  presents a graphical user interface on the touch-sensitive display  402 , providing the user access to various system objects and for conveying information. In some implementations, the graphical user interface can include one or more display objects  404 ,  406 . In the example shown, the display objects  404 ,  406 , are graphic representations of system objects. Examples of system objects include device functions, applications, windows, files, alerts, events, or other identifiable system objects. In some embodiments of the present invention, applications, when executed, provide at least some of the digital acoustic functionality described herein. 
     Typically, the mobile device  400  supports network connectivity including, for example, both mobile radio and wireless internetworking functionality to enable the user to travel with the mobile device  400  and its associated network-enabled functions. In some cases, the mobile device  400  can interact with other devices in the vicinity (e.g., via Wi-Fi, Bluetooth, etc.). For example, mobile device  400  can be configured to interact with peers or a base station for one or more devices. As such, mobile device  400  may grant or deny network access to other wireless devices. 
     Mobile device  400  includes a variety of input/output (I/O) devices, sensors and transducers. For example, a speaker  460  and a microphone  462  are typically included to facilitate audio, such as the capture of vocal performances and audible rendering of backing tracks and mixed pitch-corrected vocal performances as described elsewhere herein. In some embodiments of the present invention, speaker  460  and microphone  662  may provide appropriate transducers for techniques described herein. An external speaker port  464  can be included to facilitate hands-free voice functionalities, such as speaker phone functions. An audio jack  466  can also be included for use of headphones and/or a microphone. In some embodiments, an external speaker and/or microphone may be used as a transducer for the techniques described herein. 
     Other sensors can also be used or provided. A proximity sensor  468  can be included to facilitate the detection of user positioning of mobile device  400 . In some implementations, an ambient light sensor  470  can be utilized to facilitate adjusting brightness of the touch-sensitive display  402 . An accelerometer  472  can be utilized to detect movement of mobile device  400 , as indicated by the directional arrow  474 . Accordingly, display objects and/or media can be presented according to a detected orientation, e.g., portrait or landscape. In some implementations, mobile device  400  may include circuitry and sensors for supporting a location determining capability, such as that provided by the global positioning system (GPS) or other positioning systems (e.g., systems using Wi-Fi access points, television signals, cellular grids, Uniform Resource Locators (URLs)) to facilitate geocodings described herein. Mobile device  400  can also include a camera lens and sensor  480 . In some implementations, the camera lens and sensor  480  can be located on the back surface of the mobile device  400 . The camera can capture still images and/or video for association with captured pitch-corrected vocals. 
     Mobile device  400  can also include one or more wireless communication subsystems, such as an 802.11b/g communication device, and/or a Bluetooth™ communication device  488 . Other communication protocols can also be supported, including other 802.x communication protocols (e.g., WiMax, Wi-Fi, 3G), code division multiple access (CDMA), global system for mobile communications (GSM), Enhanced Data GSM Environment (EDGE), etc. A port device  490 , e.g., a Universal Serial Bus (USB) port, or a docking port, or some other wired port connection, can be included and used to establish a wired connection to other computing devices, such as other communication devices  400 , network access devices, a personal computer, a printer, or other processing devices capable of receiving and/or transmitting data. Port device  490  may also allow mobile device  400  to synchronize with a host device using one or more protocols, such as, for example, the TCP/IP, HTTP, UDP and any other known protocol. 
       FIG. 5  illustrates respective instances ( 501  and  520 ) of a portable computing device such as mobile device  400  programmed with user interface code, pitch correction code, an audio rendering pipeline and playback code in accord with the functional descriptions herein. Device instance  501  operates in a vocal capture and continuous pitch correction mode, while device instance  520  operates in a listener mode. Both communicate via wireless data transport and intervening networks  504  with a server  512  or service platform that hosts storage and/or functionality explained herein with regard to content server  110 ,  210 . Captured, pitch-corrected vocal performances may (optionally) be streamed from and audibly rendered at laptop computer  511 . 
     Other Embodiments 
     While the invention(s) is (are) described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention(s) is not limited to them. Many variations, modifications, additions, and improvements are possible. For example, while pitch correction vocal performances captured in accord with a karaoke-style interface have been described, other variations will be appreciated. Furthermore, while certain illustrative signal processing techniques have been described in the context of certain illustrative applications, persons of ordinary skill in the art will recognize that it is straightforward to modify the described techniques to accommodate other suitable signal processing techniques and effects. In particular, where implementations and/or illustrative applications have been described relative to plug-ins and Auto-Tune® audio processing techniques developed by Antares Audio Technologies and popularized by performance effects of artists such as T-Pain, persons of ordinary skill in the art will recognize, based on the description herein, that it is straightforward to modify the described techniques to accommodate other suitable signal processing techniques and effects. 
     Embodiments in accordance with the present invention may take the form of, and/or be provided as, a computer program product encoded in a machine-readable medium as instruction sequences and other functional constructs of software, which may in turn be executed in a computational system (such as a iPhone handheld, mobile device or portable computing device) to perform methods described herein. In general, a machine readable medium can include tangible articles that encode information in a form (e.g., as applications, source or object code, functionally descriptive information, etc.) readable by a machine (e.g., a computer, computational facilities of a mobile device or portable computing device, etc.) as well as tangible storage incident to transmission of the information. A machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., disks and/or tape storage); optical storage medium (e.g., CD-ROM, DVD, etc.); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions, operation sequences, functionally descriptive information encodings, etc. 
     In general, plural instances may be provided for components, operations or structures described herein as a single instance. Boundaries between various components, operations and data stores are somewhat arbitrary, and particular operations are illustrated in the context of specific illustrative configurations. Other allocations of functionality are envisioned and may fall within the scope of the invention(s). In general, structures and functionality presented as separate components in the exemplary configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements may fall within the scope of the invention(s).