Audio Technology / Analysis and Delivery / Preparing files for analysis and delivery...

96,000 Hz or 48,000 Hz/24-bit PCM audio files are not suitable for acoustic analysis or online delivery. In order to prepare files for acoustic analysis, several digital signal processing (DSP) techniques should be used. First, the files have to be downsampled to 11,025 Hz and their resolution should be changed to 16 bits. The downsampling process should always include the use of anti-aliasing filters, and the resolution change should include dithering to minimize the effects of quantization noise. Both Sonic Foundry Sound Forge 5.0 and BIAS Peak VST offer adequate DSP tools to do that. The Nyquist theorem guarantees that the frequency response of a 11,025 Hz is exactly half that value. This is adequate to analyze most speech sounds. If we are dealing with female and child voices, a higher sample rate (e.g., 22,000 Hz) may be used to make sure that the spectrum contains higher frequency transient sounds.