1. Technical Field
The present invention relates to a system and method for generating voice messages from pre-recorded audio segments. Individual pre-recorded audio segments are dynamically cross-faded during playback of audio messages synthesized from a plurality of such audio segments. Dynamically cross fading the sound segments speeds up the playback time of the voice messages and provides more natural sounding voice messages.
2. Related Art
In many automated systems in which a human user must interact with a computer through an audio interface, the automated system communicates with the user via audible voice prompts. Such voice prompts are typically created by chaining together multiple pre-recorded audio segments. For example, an automated telephone information service communicates telephone numbers to a requester by sequentially playing audio files representing each digit of a telephone number. Similarly, most voice recognition systems require feedback to the user. Typically such feedback is in the form of audio voice prompts requesting certain actions or information from the user. The content of such voice prompts is often context specific, so the system must select the appropriate pre-recorded sound segments to join together “on the fly” from among multiple pre-recorded sound segments in order to create a message that delivers the desired information, or asks for the appropriate response from the user.
Typically, such voice messages are created by simply concatenating a plurality of individual audio files and sequentially playing them back over a loudspeaker. Often the individual sound files will have short silent lead-in and exit times on each side of the actual sound portion of the audio file. When multiple files are played back, these short silent portions result in a message that sounds choppy and unnatural and takes much longer to play back than would otherwise be the case if the message were spoken by a live person. Such a delay and unnatural delivery can be a source of frustration for users of systems that employ synthesized voice prompts. Often a user must wait for the entire message prompt to be played back before being allowed to proceed with the next step in an automated transaction. The undue delay from excessively long voice prompts can be tedious and annoying.
FIG. 1 shows three typical pre-recorded sound files 10, 12, 14 representing the spoken words “six”, “seven” and “eight” respectively. Each of the sound files 10, 12, 14 includes a lead in time 16, and an exit time 18 where no actual sound is produced. FIG. 2 shows the same files concatenated together to form the sequence “six-seven-eight”. As can be seen, there are relatively long periods of silence 22 between the combined sound files. No information is provided to the user during these intervals. These delays unduly lengthen the playback time and detract from the sound quality of the resulting voice message.
FIG. 3 depicts a method of clipping audio files so that only those portions of the audio file in which sounds are actually voiced are included in synthesized voice messages. Unclipped sound segment 24 has silent lead in and exit portions 16, 18. In the clipped sound segment 26 the silent portions have been removed. As can be seen, the duration of the original unclipped file 24 is significantly longer than the clipped file 26. FIG. 4 again shows the numbers sequence “six-seven-eight” 28 but this time composed of sound segments that have been clipped in the manner shown in FIG. 3. Clipping the sound segments in this manner shortens the playback time of the three digit sequence from 2.12 seconds to 1.93 seconds. Although this represents a significant improvement over the unclipped sequence, the result is still longer and sounds choppier than when the sequence is spoken by a natural person. Thus, there remains a need for improved systems and methods for synthesizing voice messages and prompts from individual sound files. Such improved systems and methods must produce shorter more natural sounding voice messages and prompts.