[opus] Hybrid mode and Packet Loss Concealment

van Bijleveld Christian (ST-CO/ENG1.3) Christian.vanBijleveld at nl.bosch.com
Wed Nov 28 00:31:56 PST 2012


I am testing OPUS via the opus-tools package opus-tools-0.1.5-win32 (command line tool).

I have a question regarding hybrid mode:
-       I am using as input a 48 KHz sampling rate speech file, thus full band speech. I have tested several bitrates and frame sizes. According to the documentation, OPUS codec will work in hybrid mode when frame sizes of 10 or 20 ms are used, and bitrates from 40Kbps and above. However, the configuration info generated by the tool says that packets are coded either in LP mode (SILK) or MDCT mode (CELT), and I cannot see any reference to hybrid mode. Further reading the documentation, it says that the codec mode depends on, among others, the type of signal (speech vs. music) and that currently this parameter needs to be provided to the application (no automatic detection). I understand from this that by default, OPUS works in music mode. But there is no means to set the parameter to speech at least via a command line flag. How can OPUS be configured to work in speech mode for full band audio?

I also have a question regarding Packet Loss Concealment in hybrid mode:
-       the documentation describes (section 4.4) a PLC method for CELT mode and one for SILK mode. What is the PLC algorithm when OPUS works in hybrid mode?

Thanks in advance.

Met vriendelijke groeten | Best Regards,
Christian van Bijleveld

Bosch Security Systems BV
Bosch Communications Systems, BL Public Address and Conference Systems (ST-CO/ENG1.3)
P.O. Box 80 002
5600 JB  Eindhoven
The Netherlands
T. +31 (0)40 257 7076
F. +31 (0)40 257 7091
christian.vanbijleveld at nl.bosch.com<mailto:christian.vanbijleveld at nl.bosch.com>

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