>-----Original Message----- >From: Koen Vos [mailto:[email protected]] >Sent: Tuesday, April 16, 2013 8:48 PM >To: Paul Coverdale; 'Jean-Marc Valin'; 'Christian Hoene' >Cc: [email protected]; [email protected]; >[email protected] >Subject: RE: [codec] Opus comparision test plan > >Hi Paul, > >> - we need to be consistent about the input filtering. We can't use >> different bandwidths for Opus and AMR-WB. > >Nobody uses a low-pass filter to remove the frequencies between 7 and 8 >kHz in practice. So applying such a filter to test material reveals >little about real-life performance. > >Philosophically, filtering with the smaller frequency response makes >little sense either. Let's say someone built a codec that encodes only >frequencies from 1000 to 1100 Hz. When comparing that codec, should we >apply a similar narrow bandpass filter to the inputs of other codecs? >How about if two codecs encoded mutually-non-overlapping parts of the >spectrum?
In the past, a low-pass filter was typically used in codec subjective tests to mask any differences in anti-aliassing filters inherent in the codecs under test, so that the subjective opinion would be based on distortion and artifacts alone, and not confounded with bandwidth. If this isn't appropriate any more, we can take it out. >> - I don't understand the point about making sure to tell the Opus >> encoder what the percentage of loss is so it can optimize the encoding >> for it. What happens in practice when the loss percentage isn't known? > >Here I agree more with you. There may be poor implementations that >neglect to report packet loss back to the encoder. For characterization >purposes it would be interesting to measure the performance hit from >such implementations as compared to ideal implementations. Yes, I think we need to include the situation where packet loss is not reported back to the encoder. ....Paul _______________________________________________ codec mailing list [email protected] https://www.ietf.org/mailman/listinfo/codec
