AFTER is a diffusion-based generative model that creates new audio by blending two sources: one audio stream to set the style or timbre, and another input (either audio or MIDI) to shape the structure over time.

This repository is a real-time implementation of the research paper Combining audio control and style transfer using latent diffusion (read it here) by Nils Demerlé, P. Esling, G. Doras, and D. Genova. Some transfer examples can be found on the project webpage. This real-time version integrates with MaxMSP and Ableton Live through nn_tilde, an external that embeds PyTorch models into MaxMSP.

You can find pretrained models and max patches for realtime inference in the last section of this page.

After cloning this repository, you can install the dependencies for training with

pip install -r requirements

The only dependency for inference is the nn_tilde external.

1. Clone this repository to your local machine.
2. Add it to the list of Max paths (Options -> File Preferences...) with recursive subfolders enabled.
3. Download the pretrained models from the links below and place them in the same directory.

Training AFTER involves 4 separate steps, namely dataset preparation, autoencoder training, offline model training and streaming model distillation.

python prepare_dataset.py --input_path /audio/folder --output_path /dataset/path --num_signal 262144

The num_signal flag sets the duration of the audio chunks for training.

The autoencoder training is the longest part of AFTER training, and can be started with

python train_autoencoder.py --name AE_model_name --db_path /audio/folder  --config baseAE --config causal 

where db_path refers to the prepared dataset location. The flag --config causal greatly decreases the final latency of the model, but can degrade audio quality. The tensorboard logs and checkpoints are saved to /autoencoder/runs/AE_model_name.

After training, the model has to be exported to a torchscript file using

python export_autoencoder.py --name AE_model_name --step 1000000

Alternatively, you can use a pretrained RAVE model, or any streamable autoencoder compiled in a torchscript file with encode and decode methods.

Before training our diffusion model in the latent space of the Autoencoder, we pre-compute the latent embeddings to speed up training :

python update_dataset.py --emb_model_path pretrained/AE_model_name.ts --db_path /audio/folder 

Then, a training is started with

python train_diffusion.py  --name diff_model_name --db_path /dataset/path --emb_model_path pretrained/AE_model_name.ts --config base 

Different configurations are available in diffusion/configs and can be combined :

The tensorboard logs and checkpoints are saved to /diffusion/runs/model_name, and you can experiment with you trained model using the notebooks /notebooks/audio_to_audio_demo.ipynb and /notebooks/midi_to_audio_demo.ipynb.

After training the offline diffusion model, we retain the encoders from the offline training and train a streaming version of the model with :

python train_distill_diffusion.py  --name streaming_model_name --db_path /dataset/path --emb_model_path pretrained/AE_model_name.ts --pretrained_model /runs/offline_model_name/ --pretrained_model_step 1000000--config streaming

Once the training is complete, you can export the model to a torchscript file for inference in MaxMSP.

For an audio-to-audio model :

python export_streaming.py  --name streaming_model_name --step 1000000 --emb_model_path pretrained/AE_model_name_stream.ts 

For a MIDI-to-audio model :

python export_streaming_midi.py  --name streaming_midi_model_name --step 1000000 --emb_model_path pretrained/AE_model_name_stream.ts --npoly 4

where npoly sets the number for voices for polyphony. Make sure to use the streaming version of the exported autoencoder (denoted by _stream.ts).

Our MIDI-to-audio model is a 4-voice polyphonic synthesizer that produces audio for pitch and velocity, as well as a timbre target in two modes:

• Audio-based: Using the forward method, AFTER extracts timbre from an audio stream (with a 3 seconds receptive field). We’ve included audio samples from the training set in the repository.
• Manual exploration: The forward_manual method lets you explore timbre with 8 sliders, which set a position in a learned 8-dimensional timbre space.

The guidance parameter sets the conditioning strength on the MIDI input, and diffusion steps can be adjusted to improve generation quality (at a higher CPU cost).

Download our instrumental model trained on the SLAKH dataset here.

Audio Timbre Target	Manual Timbre Control

In audio-to-audio mode, AFTER extracts the time-varying features from one audio stream and applies them to the timbre of a second audio source. The guidance parameter controls the conditioning strength on the structure input, and the diffusion steps improve generation quality with more CPU load.

Download our instrumental model trained on the SLAKH dataset here.

AFTER has been applied in several projects:

• The Call by Holly Herndon and Mat Dryhurst, an interactive sound installation with singing voice transfer, at Serpentine Gallery in London until February 2, 2025.
• A live performance by French electronic artist Canblaster for Forum Studio Session at IRCAM. The full concert is available on YouTube.
• Nature Manifesto, an immersive sound installation by Björk and Robin Meier, at Centre Pompidou in Paris from November 20 to December 9, 2024.

We look forward to seeing new projects and creative uses of AFTER.