[opus] SILK-implementation some questions

Diego Alejandro Parra Guzman daparrag at correo.udistrital.edu.co
Tue Oct 10 11:10:46 UTC 2017

Dear all:

I want to formulate couple of questions about SILK codec:


I've seen the documentation to the SILK codec that is part of the OPUS
exactly the paper with title "The opus codec voice coding with opus, and
the "RFC 6716 specification of opus" . Well, I detected that in both is
defined a High-Pass filter as part of SILK; however in the paper you put
the following description:

" A high-pass (HP) filter with a variable cut frequency between 60 and 100

while form the other hand in the  RFC 6716 is defined as:

RFC 6716:
"This is a second order Auto Regressive Moving Average (i.e., with poles
and zeros) filter with a cut-off frequency around 50 Hz"

and actually both of them are implemented one is in the function
 silk_Encode  @enc_API file,  and the second is in the function hp_cutoff
@opus_encoder file.

Therefore I'm right to guess that you are using both ?  and what should
be the most convenient reference to follow the implementation of OPUS and
it is components such as CELT and SILK ?

2.  according to and just to clarify :

               +----------+    +--------+    +---------+
               |  Sample  |    | Stereo |    |  SILK   |
        ------>|   Rate   |--->| Mixing |--->|  Core   |---------->
        Input  |Conversion|    |        |    | Encoder |  Bitstream
               +----------+    +--------+    +---------+

                          Figure 21: SILK Encoder

I want to known if effectively the sample rate conversion and stereo
mixing have been implemented directly in the SILK core encoder or
instead both/or one were implemented independently? and where they are
allocated in the code ?.

I request for your help since we are working to improve OPUS in such as way
that it could be supported in very constrained devices and in low power
consumption local networks such as Bluetooth LE.

thanks so much
Best regards
Diego A parra guzman.

Diego Alejandro Parra Guzmán
Estudiante de ingeniería electrónica
Universidad distrital FJC
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