<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;">Dear list,<br><br>>> I' m studying FLAC performance, and I'd like to know how much compression can be achieved for different audio files.<br>>> <br>>>
1) It seems that for nontonal sound (wideband noise), the compression
factor is better than for compound sound (tones + nontonal components),
which is typically 2. The reason for this result could be the
following: the LPC filter is more suitable for estimating the amplitude
spectrum of non tonal information, and do not take into account the
phase contribution for each spectral component. Do you agree with me,
or do you suggest other reasons for this?<br><br>>You should also find
that lower amplitudes compress better than higher amplitudes. For
example, if "live" material with normal dynamic range is compressed by
FLAC, the ratio will be better than the same audio which has been
compressed for mastering, which raises the levels of all the material
in addition to reducing the range between quiet and loud.<br><br>If you ask why "live" material can be better compressed may be because it contains more wideband noise, which is better represented by the LPC estimator. Is this your point?<br><br><br>>Your
"wideband noise" may be gaussian or uniform distribution, and this
could greatly affect the compression. I.e. do not assume that all
noise is the same.<br><br>I didn't know that different types of noise can produce different compression ratios. Did you quantify this difference?<br><br><br>>There are probably other correlations besides
just noise vs. tones and loud vs. quiet. It seems like you may want to
do additional research.<br><br>I haven't studied about correlations, but I have decomposed sounds into tones + wideband noise. Tones were detected from the input spectrogram, and the background noise was described as white noise filtered by an LCP filter. More details can be found on this link:<br><br>http://www.cimec.org.ar/ojs/index.php/mc/article/viewFile/2711/2653<br><br><br>Best regards,<br><br>Dr. Fernando A. Marengo Rodriguez<br>Acoustics and Electroacoustics Laboratory<br>National University of Rosario<br>Rosario, Argentina</td></tr></table><br>
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