[opus] manual pitch modification

[Mark Harvilla]

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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