[opus] manual pitch modification

[Jean-Marc Valin]

Hi Mark,

I'm not sure what you're trying to achieve with the pitch modification,
but in most cases (e.g. pitch shifting), there are tools that can do
that much better than trying to hack a decoder. Changing it in the Opus
decoder will at best give you pretty mediocre quality.

Cheers,

	Jean-Marc

On 30/06/17 09:01 PM, Mark Harvilla wrote:
> Hello,
> 
> When used in SILK mode, is there a way to manually modify the pitch (F0)
> of the speech signal before resynthesizing during Opus decoding?
> 
> In the below, we have modified the pitch lags of (4), e.g., with a
> constant scaling factor 0.5 to decrease the pitch of the voice by one
> octave. However, the result was perceptually the same as without
> modifying the pitch lags.
> 
>         +---------+    +------------+
>      -->| Range   |--->| Decode     |---------------------------+
>       1 | Decoder | 2  | Parameters |----------+       5        |
>         +---------+    +------------+     4    |                |
>                             3 |                |                |
>                              \/               \/               \/
>                        +------------+   +------------+   +------------+
>                        | Generate   |-->| LTP        |-->| LPC        |
>                        | Excitation |   | Synthesis  |   | Synthesis  |
>                        +------------+   +------------+   +------------+
>                                                ^                |
>                                                |                |
>                            +-------------------+----------------+
>                            |                                      6
>                            |   +------------+   +-------------+
>                            +-->| Stereo     |-->| Sample Rate |-->
>                                | Unmixing   | 7 | Conversion  | 8
>                                +------------+   +-------------+
> 
> 
> Thanks,
> -Mark
> 
> 
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