Then a second higher amplitude tone that appears. They consist of one low-amplitude tone that pulses on and off, and These clips illustrate frequency masking effects in perceptual codecs. The third set of clips illustrates what happens when you try and code music with a low bitrate speech codec. Original PCM 16-bit linear file (128Kb/s).Happening in CELP and G.729, but the residue coding mostly manages to Wrong voiced/unvoiced decision by the codec. Notice in LPC how the background noise sometimes triggers the
The next set of clips illustrate how well these codecs perform in a noiseĮnvironment. "s" in "is" which is pronouced like a "z" simultaneously voiced and (tool) and "G" (grab), which are part voiced, part unvoiced, and the Which are unvoiced sounds, some difficult consonants "b" (big), "t" Has a good mix of sounds including "th" (lathe) and "sh" (dish, sugar) These first set of clips give a basic comparison of speech codecs. Higher frequency quantization noise appears. wav file [48KHz sampled, 8 bit,Īs the number of levels is decreased, more square edges are introduced, and The difference between the second and third clips is aliasing noise - sounds above 4KHz being sampled at 8KHz, and appearing as aliasing noise below 4KHz.Ī simple tone, quantized to 256 linear levels, 16 linear levels, and 4 linear Downsampled to 8KHz using a 4KHz anti-aliasing (low-pass) filter:.In the last sample, aliasing is clear, as for the middle part of the clip highįrequencies above 4KHz have been "folded" back into the lower 4KHz region. Downsampled to 8KHz by simply taking one sample in six:.Downsampled to 8KHz using a 4KHz anti-aliasing filter:.Tone that increases from 50Hz to 8KHz, then decreases back to 50KHz again. These sound clips illustrate the effects of sampling and quantization noise Might interact badly with the compression artifacts I want you to hear. (uncompressed PCM, either 8-bit or 16-bit) because any further compression I suggesting listening in a fairly quiet environment, with a good set of The speakers in the lecture theatresĪren't the best, so some of the artifacts were not as clear as they might be.
This page gives all the audio samples I played during the GZ05 lectures, and aįew more that there wasn't time for. GZ05: Multimedia Systems: Samples GZ05: Multimedia Systems: Audio Samples
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