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Audio Demonstrations.docx

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Paul Faure

October 2 , 2013 Psych 3A03: Audition Audio Demonstrations Measuring Noise Amplitude - 10log (N )0= 10log(TP) – 10log(BW) White Noise Versus Pink Noise - Pink = -3dB per doubling Resonators - Damped sinusoidal motion: a free vibration in response to a single input force - Standing waves develop as a result of continuous forced vibrations from external force - Most acoustic events result from forced or driven vibrations - Objects naturally vibrate at their natural frequency Frequency Selective Attenuation - Filters perform a frequency selective attenuation on a sound - Filters work on both simple sounds and complex sounds Filter Cutoff (fc) = -3dB Frequency - The cutoff frequency of a filter is the frequency where the signal energy decreases by one half (i.e. -3dB) - The f cs the frequency where the output energy of the gilter drops to ½ of the input energy - Band pass and band reject fiters have both a low pass and high pass cutoff frequency Filter Rate of Attenuation (Roll-Off) - Filter cutoff frequency defines ½ power (-3dB) point - The amount of attenuation is known as the roll-off rate - Filter roll-off rate is measured in dB per octave (=slope) - Octave = frequency doubling - Roll-off rate is in decibels of attenuation per doubling of frequency starting from the filter’s cutoff frequency (f )c - E.g. 6dB/octave; 10dB/octave Filter Bandwidth - A filter’s bandwidth is computed as the frequency range or difference between the high pass and low pass cutoff frequencies - BW = f -lp (hpw pass cutoff frequency – high pass cutoff frequency) - The bandwidth determines the range of frequencies that can pass through a filter with little or no attenuation - Bandwidth is always a positive number - Broadband filter: wide BW - Narrowband filter: narrow BW (this is a relative comparison) Filters Also Change the Time Domain - Filters also introduce phase delays to signals that pass through the filters - Some frequencies may experience more of a phase shift than others - To fully describe a filter we must specify: 1. Filter type (e.g. low, band, high pass, or bad reject) 2. Cutoff frequencies (f ) c 3. Filter bandwidth (BW) and center frequency (CF – middle position of the filter) 4. Roll-off rate of filter attenuation (dB/octave) 5. Phase delay at each frequency (phase spectrum is very useful for this) Equivalent Rectangular Bandwidth (ERB) - This is an alternative way of specifying the bandwidth of an auditory filter - The equivalent rectangular bandwidth is simply the bandwidth of a rectangular filter with the same height and frequency area as an auditory or electrical filter - We will discuss ERB’s later in the course More on Filters - The characteristics of a filter can be obtained by conducting a Fourier analysis of the filter’s resp
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