signal Speech Signal Processing

Speech Production

Speech Waveform Characteristics
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Loudness Voiced/Unvoiced. Pitch.
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Fundamental frequency. Formants.

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Spectral envelope.
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Speech Waveform Characteristics
Voiced Unvoiced

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s

Short-Time Speech Analysis
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Segments (or frames, or vectors) are typically of length 20 ms.
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Speech characteristics are constant. Allows for relatively simple modeling.

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Often overlapping segments are extracted.

The Spectrogram
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A classic analysis tool.
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Consists of DFTs of overlapping, and windowed frames.

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Displays the distribution of energy in time and frequency.

A spectrogram

Short time ACF
/m/ /ow/ /s/

ACF

|DFT|

Sound Propagation
Sound propagates from the source to the receiver through a combination of four main propagation modes:
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direct propagation path reflection from walls diffraction around objects refraction due to temperature differences in the layers of air. For that reason sound is delayed and attenuated by different amounts.

Reflection
One happens when a sound wave encounters a medium with different impedance from which it is travelling in, for example when the sound propagating in the air hits the walls of a room (fig. 1). Sound reflects from walls, objects, etc. Acoustically, reflection results in: Sound reverberation - for small round-trip delays (less than 100 ms), Echo - for longer round-trip delays. fig. 1

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Diffraction
One is the bending of waves around objects and the spreading out of waves beyond openings ( figure 2). In order for this effect to be observed the size of the object or gap must be comparable to or smaller than the wavelength of the waves. Each opening acts as a new source of sound, and the waves from these secondary sources can act constructively and destructively. ● If the