Use in-place operation to save memory (facebookresearch#501)

* Use in-place operation to save memory

* Update release.md

demucs/__init__.py

@@ -4,4 +4,4 @@
 # This source code is licensed under the license found in the
 # LICENSE file in the root directory of this source tree.
 
-__version__ = "4.0.1a1"
+__version__ = "4.0.1a2"

demucs/separate.py

@@ -165,11 +165,13 @@ def main(opts=None):
         wav = load_track(track, model.audio_channels, model.samplerate)
 
         ref = wav.mean(0)
-        wav = (wav - ref.mean()) / ref.std()
+        wav -= ref.mean()
+        wav /= ref.std()
         sources = apply_model(model, wav[None], device=args.device, shifts=args.shifts,
                               split=args.split, overlap=args.overlap, progress=True,
                               num_workers=args.jobs, segment=args.segment)[0]
-        sources = sources * ref.std() + ref.mean()
+        sources *= ref.std()
+        sources += ref.mean()
 
         if args.mp3:
             ext = "mp3"

docs/release.md

@@ -11,6 +11,8 @@ Made diffq an optional dependency, with an error message if not installed.
 
 Added output format flac (Free Lossless Audio Codec)
 
+Optimize codes to save memory
+
 ## V4.0.0, 7th of December 2022
 
 Adding hybrid transformer Demucs model.