SFS/WASP Help File
WASP is a program for the recording, display and analysis of speech. With WASP you can record and replay speech signals, save them and reload them from disk, edit annotations, display spectrograms and a fundamental frequency track, and print the results.
WASP is a simple application that is complete in itself but which is also designed to be compatible with the Speech Filing System (SFS) tools for speech research.
Other menu options
Other replay commands
Cursors and Annotations
With a waveform loaded and displayed, you can set left and right cursors using the left and right mouse buttons. The left cursor is blue, the right cursor is green. These cursors indicate the start and stop time for various operations:
To enter an annotation, first press the letter 'A' (for annotation at the left cursor) or 'B' (for annotation at the right cursor) then type in the label and press the RETURN key when done. You will see the characters you type appear in the status bar. You can edit a label being entered with the BACKSPACE key. You can cancel an annotation entry by pressing ESCAPE. You can change an annotation by entering a new annotation at the same place. You can delete an annotation by entering an empty annotation at the same place.
The time at which the left and right cursors are located is displayed in the status bar. For convenience, the interval between the cursors is also displayed, as well as the reciprocal of that interval. These may be of use to estimate durations and frequencies from the signal.
You can remove a cursor by clicking the mouse button twice at the same location.
Information about the location of the cursors is displayed at the right of the status bar. The times of the left and right cursor are displayed, also the interval between them expressed in seconds and Hertz, and finally the value of the fundamental frequency track under the left cursor.
Most PCs have two input lines, one designed for a microphone input and one designed for a 'line' level input (from e.g. a tape recorder). Some PCs are also able to record output from audio CDs played in the computer. Once your signal source is connected to the computer, you need to select it using the Volume Control application. This can be found under the Start/Programs/Accessories/Multimedia menu on Windows 95/98/NT systems.
To record from a microphone:
In the WASP record dialogue, you can adjust the recording quality by changing the sampling rate. The default rate of 16000 samples per second with 16-bit resolution has been chosen to be most useful for the production of speech spectrograms. Not all PCs support acquisition at 16000 samples per second. You may find it necessary to record at 22050 samples/second or at 11025 samples/second. WASP does not support recording using old 8-bit resolution cards although it can load 8-bit waveforms recorded by other applications.
A waveform is a graph of signal amplitude (on the vertical axis) against time (on the horizontal axis). Conventionally, the zero line is taken to mean no input: in terms of a microphone this would imply that the sound pressure at the microphone was the same as atmospheric pressure. Positive and negative excursions can then be considered pressure fluctuations above and below atmospheric pressure. For speech signals these pressure fluctuations are very small, typically less than +/- 1/1000000 of atmospheric pressure. The amplitude scale used on waveform displays merely records the size of the quantised amplitude values captured by the Analogue-to-Digital converter in the PC. These have a maximum range of -32,768 to +32,767. If you observe values close to these on the display, it is likely that the input signal is overloaded.
A spectrogram is a display of the frequency content of a signal drawn so that the energy content in each frequency region and time is displayed on a grey scale. The horizontal axis of the spectrogram is time, and the picture shows how the signal develops and changes over time. The vertical axis of the spectrogram is frequency and it provides an analysis of the signal into different frequency regions. You can think of each of these regions as comprising a particular kind of building block of the signal. If a building block is present in the signal at a particular time then a dark region will be shown at the frequency of the building block and the time of the event. Thus a spectrogram shows which and how much of each building block is present at each time in the signal. The building blocks are, in fact, nothing more than sinusoidal waveforms (pure tones) occuring with particular repetition frequencies. Thus the spectrogram of a pure tone at 1000Hz will consist of a horizontal black line at 1000Hz on the frequency axis. Such a signal only contains a single type of building block: a sinusoidal signal at 1000Hz.
Wideband spectrograms use coarse-grained regions on the frequency axis. This has two useful effects: firstly it means that the temporal aspects of the signal can be made clear - we can see the individual larynx closures as vertical striations on a wide band spectrogram; secondly it means that the effect of the vocal tract resonances (called formants) can be seen clearly as black bars between the striations - the resonances carry on vibrating even after the larynx pulse has passed though the vocal tract. The bandwidth for the wideband display is fixed at 300Hz.
Narrowband spectrograms use fine-grained regions on the frequency axis. This has two main effects: firstly fine temporal detail is lost which means that the individual larynx pulses are no longer seen; secondly fine frequency structure is brought out consisting of the harmonics of the larynx vibration as filtered by the resonances of the vocal tract. This kind of display is most useful for the study of slowly varying properties of the signal, such as fundamental frequency. The bandwidth for the narrowband display is fixed at 45Hz.
Fundamental frequency track
The fundamental frequency track shows how the pitch of the signal varies with time. Pitch is properly a subjective attribute of the signal, but it is closely related to the repetition frequency of a periodic waveform. Thus if a signal has a waveform shape that repeats in time (such as a simple vowel) then we perceive a pitch related to how long the signal takes to repeat. A signal with a long repetition period (low repetition frequency) has a low pitch, while a signal with a short repetion period (high repetition frequency) has a high pitch. The proper name for the repetition frequency of periodic waveforms is called the fundamental frequency because this frequency has an important role in determining which frequency components are present in a periodic signal. A signal that is periodic at F Hz, can only have frequency components at F, 2F, 3F, ...; these are called the harmonic components (or just harmonics) of the signal.
Note that all algorithms for estimating the fundamental frequency from the speech signal do fail on some occasions. This is because of the complexity of the speech signal and the influence of any interfering noise. Where the algorithm is unable to determine any effective periodicity in the signal, no fundamental frequency estimate is displayed. The algorithm is optimised for human speech signals, so may fail to find the correct pitch for musical instruments and other sounds.
Annotations are simply text labels that are associated with a particular time in the speech signal. They may be used to mark the boundaries between words or phonetic segments or to indicate the presence of specific events. Annotations are automatically saved and restored with the speech signal when you choose to use SFS format files. To perform additional processing with these labels you need to use some of the SFS tools such as anlist, andict, or sml. See the SFS Web Pages for more information.
Want to learn more?
If you find the study of speech interesting and would like to know more, why not visit the Internet Institute of Speech and Hearing at www.speechandhearing.net ? There you will find tutorials, reference material, laboratory experiments and contact details of professional organisations.
Please send suggestions for improvements and reports of program faults to SFS@phon.ucl.ac.uk.
Please note that we are unable to provide help with the use of this program.
WASP is not public domain software, its intellectual property is owned by Mark Huckvale, University College London. However WASP may be used and copied without charge as long as the program and help file remain unmodified and continue to carry this copyright notice. Please contact the author for other licensing arrangements. WASP carries no warranty of any kind, you use it at your own risk.
Wasp contains fundamental frequency estimation code developed by David Talkin and Derek Lin as part of the Entropic Signal Processing System and is used under licence from Microsoft.
Wasp artwork from www.webdog.com.au with thanks.
|© 2007 Mark Huckvale University College London||Version 1.6 August 2007|