Doc: references for `lfilter` implementation (#3734)

* add golf and dynonet paper

* doc: add references

* add EOF

* fix: line too long

* remove line end space

* remove indentation
Co-authored-by: moto <855818+mthrok@users.noreply.github.com>

---------
Co-authored-by: moto <855818+mthrok@users.noreply.github.com>

docs/source/refs.bib

@@ -598,3 +598,38 @@ booktitle	= {International Conference on Acoustics, Speech and Signal Processing
   year={1982},
   publisher={Elsevier}
 }
+
+@inproceedings{ismir_YuF23,
+  author       = {Chin{-}Yun Yu and
+                  Gy{\"{o}}rgy Fazekas},
+  editor       = {Augusto Sarti and
+                  Fabio Antonacci and
+                  Mark Sandler and
+                  Paolo Bestagini and
+                  Simon Dixon and
+                  Beici Liang and
+                  Ga{\"{e}}l Richard and
+                  Johan Pauwels},
+  title        = {Singing Voice Synthesis Using Differentiable {LPC} and Glottal-Flow-Inspired
+                  Wavetables},
+  booktitle    = {Proceedings of the 24th International Society for Music Information
+                  Retrieval Conference, {ISMIR} 2023, Milan, Italy, November 5-9, 2023},
+  pages        = {667--675},
+  year         = {2023},
+  url          = {https://doi.org/10.5281/zenodo.10265377},
+  doi          = {10.5281/ZENODO.10265377},
+  timestamp    = {Mon, 18 Dec 2023 11:23:01 +0100},
+  biburl       = {https://dblp.org/rec/conf/ismir/YuF23.bib},
+  bibsource    = {dblp computer science bibliography, https://dblp.org}
+}
+
+@article{forgione2021dynonet,
+  title={dynoNet: A neural network architecture for learning dynamical systems},
+  author={Forgione, Marco and Piga, Dario},
+  journal={International Journal of Adaptive Control and Signal Processing},
+  volume={35},
+  number={4},
+  pages={612--626},
+  year={2021},
+  publisher={Wiley Online Library}
+}

src/torchaudio/functional/filtering.py

@@ -998,7 +998,8 @@ else:
 
 
 def lfilter(waveform: Tensor, a_coeffs: Tensor, b_coeffs: Tensor, clamp: bool = True, batching: bool = True) -> Tensor:
-    r"""Perform an IIR filter by evaluating difference equation.
+    r"""Perform an IIR filter by evaluating difference equation, using differentiable implementation
+    developed independently by *Yu et al.* :cite:`ismir_YuF23` and *Forgione et al.* :cite:`forgione2021dynonet`.
 
     .. devices:: CPU CUDA