docs(vc): add page on voice conversion

[ci skip]

README.md

@@ -235,7 +235,7 @@ tts.tts_to_file(text="Ich bin eine Testnachricht.", file_path=OUTPUT_PATH)
 
 #### Voice conversion (VC)
 
-Converting the voice in `source_wav` to the voice of `target_wav`
+Converting the voice in `source_wav` to the voice of `target_wav`:
 
 ```python
 tts = TTS("voice_conversion_models/multilingual/vctk/freevc24").to("cuda")
@@ -247,9 +247,13 @@ tts.voice_conversion_to_file(
 ```
 
 Other available voice conversion models:
+- `voice_conversion_models/multilingual/multi-dataset/knnvc`
 - `voice_conversion_models/multilingual/multi-dataset/openvoice_v1`
 - `voice_conversion_models/multilingual/multi-dataset/openvoice_v2`
 
+For more details, see the
+[documentation](https://coqui-tts.readthedocs.io/en/latest/vc.html).
+
 #### Voice cloning by combining single speaker TTS model with the default VC model
 
 This way, you can clone voices by using any model in 🐸TTS. The FreeVC model is

docs/source/inference.md

@@ -16,6 +16,7 @@ Coqui TTS provides three main methods for inference:
 
 ```{toctree}
 :hidden:
+vc
 server
 marytts
 ```

docs/source/models/xtts.md

@@ -182,7 +182,7 @@ To use the model API, you need to download the model files and pass config and m
 If you want to be able to `load_checkpoint` with `use_deepspeed=True` and **enjoy the speedup**, you need to install deepspeed first.
 
 ```console
-pip install deepspeed==0.10.3
+pip install deepspeed
 ```
 
 #### Inference parameters

docs/source/vc.md

@@ -0,0 +1,84 @@
+# Voice conversion
+
+## Overview
+
+Voice conversion (VC) converts the voice in a speech signal from one speaker to
+that of another speaker while preserving the linguistic content. Coqui supports
+both voice conversion on its own, as well as applying it after speech synthesis
+to enable multi-speaker output with single-speaker TTS models.
+
+### Python API
+
+Converting the voice in `source_wav` to the voice of `target_wav` (the latter
+can also be a list of files):
+
+```python
+from TTS.api import TTS
+
+tts = TTS("voice_conversion_models/multilingual/vctk/freevc24").to("cuda")
+tts.voice_conversion_to_file(
+  source_wav="my/source.wav",
+  target_wav="my/target.wav",
+  file_path="output.wav"
+)
+```
+
+Voice cloning by combining TTS and VC. The FreeVC model is used for voice
+conversion after synthesizing speech.
+
+```python
+
+tts = TTS("tts_models/de/thorsten/tacotron2-DDC")
+tts.tts_with_vc_to_file(
+  "Wie sage ich auf Italienisch, dass ich dich liebe?",
+  speaker_wav=["target1.wav", "target2.wav"],
+  file_path="output.wav"
+)
+```
+
+Some models, including [XTTS](models/xtts.md), support voice cloning directly
+and a separate voice conversion step is not necessary:
+
+```python
+tts = TTS("tts_models/multilingual/multi-dataset/xtts_v2").to("cuda")
+wav = tts.tts(
+  text="Hello world!",
+  speaker_wav="my/cloning/audio.wav",
+  language="en"
+)
+```
+
+### CLI
+
+```sh
+tts --out_path output/path/speech.wav \
+    --model_name "<language>/<dataset>/<model_name>" \
+    --source_wav <path/to/speaker/wav> \
+    --target_wav <path/to/reference/wav1> <path/to/reference/wav2>
+```
+
+## Pretrained models
+
+Coqui includes the following pretrained voice conversion models. Training is not
+supported.
+
+### FreeVC
+
+- `voice_conversion_models/multilingual/vctk/freevc24`
+
+Adapted from: https://github.com/OlaWod/FreeVC
+
+### kNN-VC
+
+- `voice_conversion_models/multilingual/multi-dataset/knnvc`
+
+At least 1-5 minutes of target speaker data are recommended.
+
+Adapted from: https://github.com/bshall/knn-vc
+
+### OpenVoice
+
+- `voice_conversion_models/multilingual/multi-dataset/openvoice_v1`
+- `voice_conversion_models/multilingual/multi-dataset/openvoice_v2`
+
+Adapted from: https://github.com/myshell-ai/OpenVoice