Acoustics 2 Flashcards
What is a low pass filter?
A filter that only transfers sound energy at frequencies below a certain cut-off, and blocks energy above said frequency
What is a high pass filter?
A filter than transfers sound energy at frequencies higher than a certain cut-off, and blocks sound energy below said frequency
What is a band pass filter?
A filter that combines both low and high pass filters, thus transmitting sound energy within a particular frequency range/ band
Define bandwidth in the context of band pass filters.
A bandwidth is the range of frequencies passed by a filter
Describe the effect of changing the bandwidth on the level of frequency and temporal detail obtained from spectral analysis (i.e. time-frequency trade-off)
Fast Fourier Transforms (FFTs) that visually display sound signals operate on a window of analysis. This window is related to the bandwidth of the filtering. Spectral analysis filtering with narrow bandwidths have a high level of frequency resolution, but requires a long analysis window to distinguish freqeuncies are they are more detailed. This means that the temporal resolution of the analysis is limited and rapid changes in the spectrum will not be visivle as they are shorter than the analysis window
Describe the relationship between bandwidth and the temporal window of analysis.
The bandwidth size and the temporal window of analysis have an inverse relationship. The wider the bandwidth size the more limited the temporal window of analysis is, and vice versa.
What are the definitions and axes for a time-amplitude waveform?
A time-amplitude waveform represents how the amplitude of a signal varies over time (x-axis is time, y-axis is amplitude)
What is the definition of a spectrum and what are its axes?
A spectrum represents frequencies in a signal, showing the amplitudes of different frequency components (x-axis is frequency, y-axis is amplitude)
What is the definition of a spectrogram and what are its axes?
Spectrograms are a visual representation of the spectrum as it varies with time (x-axis is time, y-axis is frequency)
Identify the features of speech signals that can and cannot be seen in a narow-band spectrogram.
Voiced sections of speech can be seen due to good frequency resolution, whilst glottal pulsing of vocal cords are not visible due to poor temporal resolution
Identify the features of speech signals that can and cannot be seen in a broad-band spectrogram.
Glottal pulsing and vowel formant are clear due to good temporal resolution, whilst individual harmonics are not visible due to poor frequency resolution
Define resonance and the resonance properties of a closed end tube.
1) Resonace is the amplification of a vibration from an original source through an acoustic resonator.
2) The air inside of a closed end tube will resonate at frequencies relating to the length of the tube itself.
3) The lowest resonance frequency will be 4 times the length of the tube, followed by higher formants occuring at odd multiples of the lowest resonance frequency.
4) Only frequencies that match the resonance frequencies of the tube will get amplified, the rest of the sound frequencies will not.
Describe the source filter theory of speech production, including the 2 main components (i.e. the source and the filter).
1) Sound at larynx is usually periodic (i.e. harmonic spectrum with vibrations occurring at every multiple of the fundamental frequency)
2) This harmonic spectrum gets passed through the vocal tract as it acts as a closed end tube (i.e. acoustic resonator)
3) Only frequencies that match the vocal tract get amplified (i.e. vocal tract acts as filter to sound energy generated at larynx)
4) Therefore, the source is the sound energy generate da tthe larynx, and the filter is the vocal tract amplifying certain frequencies whilst not amplifying others
