RWCP Sound Scene Database in Real Acoustical Environments
Calculation method for low path filter and down sampling (48kHz->16kHz)

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Kazuo Hiyane and Jun Iio, Mitsubishi Research Institute,Inc.

The 48 kHz of the sampling frequency adopted in the recording is satisfactory for covering the audio-frequency range. However, in actual implemention and research, a 16 kHz sampling is often used. Thus, down sampling is carried out from 48 kHz to 16 kHz data.

The SPTK, a speech sound signal processing tool kit provided free of charge by the Tokyo Institute of Technology, contains a filter to make the sampling frequency to 1/ 2 or 4/ 5 and no filter for 1/3 necessary herewith. A filter index was determined by MATLAB to make calculation for down sampling and low path filter by the C program.

To get a high cutoff characteristic and a flat characteristic, a FIR filter was yielded by the following MATLAB command.

firl( 300, 7.7/24, 'STOP' )
The cutoff frequency is 7.7 kHz in harmonics of the order 300. As known from the graph of the frequency characteristic measured by the following computer simulation, in spite of the cutoff characteristic of -60 dB, ripples are satisfactorily small at 0.018 dB (= 1.0021.)

Frequency characteristic of low path filter
Frequency characteristic of low path filter

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