I think the effect of compression on sound quality it is still a debatable
question. It is very important to know which sound features may be affected
by compression and how the acoustic context may affect the compression
algorithm's behaviour. I made some tests with MP3 encoding/decoding and
several effects can be easily detected by hearing or by spectrographic
analysis. Of course, with MP3 the compression is scalable and alterations
increase with increasing the compression factor (which corresponds to
reducing the bit rate).
The MP3 works both in frequency and in time; by using algorithms based on
both frequency and time masking, it can cut a short segment of a signal if
it is just after a strong sound. This happens with sperm whale clicks: if
they are very loud, after each click the spectrogram shows a short segment
of silence (it is not noticeable by hearing, but it may cut some important
features we measure in the 10 ms after a click!).
I don't know how ATRAC behaves. As I can't afford the buy of an MD recorder
only for this testing, I would like to know if there is some software able
to perform ATRAC coding/decoding I could use for doing some tests.
Any information will be appreciated,
regards,
Gianni
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Gianni Pavan
Email
Centro Interdisciplinare di Bioacustica e Ricerche Ambientali
Universita' degli Studi di Pavia
Via Taramelli 24, 27100 PAVIA, ITALIA
Tel/Fax +39-0382-525234 Laboratori
Tel/Fax +39-0382-526208 Segreteria
Web http://www.unipv.it/cibra
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