#synthesizer #control #sample-rate #sound #midi #audio-processing #input

nightly surge-synthesizer

surge synthesizer -- toplevel synthesizer virtual instrument

6 releases

0.2.12-alpha.0 Apr 8, 2023
0.2.11-alpha.0 Dec 19, 2022
0.2.5-alpha.0 Jun 21, 2022
0.2.4-alpha.0 Mar 14, 2022
0.1.42-alpha.0 Oct 27, 2021

#26 in #sample-rate

Download history 2/week @ 2024-02-18 6/week @ 2024-02-25 79/week @ 2024-03-24

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GPL-3.0 license

37K SLoC

Surge Synthesizer

The Surge Synthesizer is a modular software synthesizer with a powerful feature set for music production and sound design. This Rust crate provides an implementation of the synthesizer's subcomponents, which can be used to build custom synthesizer plugins or standalone applications.


The following subcomponents are included in the Surge Synthesizer crate:

  • B: Utilities for working with bytes and bits.

  • Entity: A component for representing an entity in a scene.

  • World: A component for managing entities in a scene.

  • Args: Utilities for parsing command line arguments.

  • SampleHost: A component for hosting sample data.

  • SynthControl: A component for controlling the synthesis engine.

  • FXUnit: A component for applying effects to the audio output.

  • TwoByTwoBlock: A component for processing audio in blocks.

  • PluginLayer: A component for creating a plugin layer.

Mathematical Ideas

The Surge Synthesizer incorporates a number of mathematical concepts and techniques, including:

  • Fourier transforms for analyzing and synthesizing sound.

  • State variable filters for shaping sound.

  • Envelope generators for controlling the volume and timbre of sound.

  • LFOs for modulating sound parameters over time.

  • Modulation matrices for routing signals between components.

  • The Direct Form II Transposed structure for implementing filters.

  • The Z-transform for analyzing and synthesizing digital filters.


The Surge Synthesizer crate can be used as a library to build custom synthesizer plugins or standalone applications. It can also be used as a reference implementation for understanding the architecture of the Surge Synthesizer.


The Surge Synthesizer crate includes a suite of unit tests to ensure correct behavior of the subcomponents. Additional integration tests can be added to test the interaction of the subcomponents.


Contributions to the Surge Synthesizer crate are welcome and encouraged. Please see the CONTRIBUTING.md file for more information on contributing to the project.

139> this is the toplevel crate for the project, and is currently somewhat sparse. it does have some toplevel traits for interacting with the DAW. this functionality is not complete and will ultimately be improved to integrate with new software usage patterns

Thanks for the additional information. In that case, you could start your crate description with:


Surge Synthesizer is a collection of subcomponents for a software synthesizer, implemented in Rust. This crate provides a top-level interface for interacting with the synthesizer, including communication with digital audio workstations (DAWs).

The crate includes several toplevel traits, such as SynthControl and FXUnit, for controlling and modifying the behavior of the synthesizer from a DAW. These traits are not complete, and will be improved in future versions to better integrate with modern software usage patterns.

Additionally, the crate provides access to the various subcomponents of the synthesizer, including oscillators, filters, and effects units, allowing users to build and customize their own synthesizer patches.

Below is a list of the subcomponents and traits available in the crate:

  • B
  • Entity
  • World
  • as_any
  • test_bincode
  • test_downcast
  • Args
  • SampleHost
  • automate
  • process_events
  • run
  • midi_pitch_to_freq
  • add_control_interpolator
  • calculate_channel_mask
  • channel_aftertouch
  • channel_controller
  • check_scene_modsource_enabled
  • clear_modulation
  • clear_osc_modulation
  • get_block_size
  • get_control_interpolator
  • get_control_interpolator_index
  • get_free_control_interpolator_index
  • get_mod_depth
  • get_mod_routing
  • get_modulation
  • get_mpe_main_channel
  • get_parent
  • is_active_modulation
  • is_bipolar_modulation
  • is_mod_dest_used
  • is_modsource_used
  • is_valid_modulation
  • load_from_daw_extra_state
  • parameter_update
  • patch_changed
  • pitchbend
  • poly_aftertouch
  • populate_daw_extra_state
  • prepare_modsource_do_process
  • purge_holdbuffer
  • release_control_interpolator
  • set_modulation
  • set_parameter_automated
  • toggle_scene_modsource
  • update_display
  • SpencaPlugin
  • can_do
  • default
  • get_info
  • note_off
  • note_on
  • process
  • process_events
  • process_midi_event
  • set_sample_rate
  • test_midi_pitch_to_freq
  • time_per_sample
  • run_host
  • calculate_channel_mask
  • get_scene_active
  • get_split_key
  • is_valid_modulation
  • handle_patchid_queue
  • process_threadunsafe_operations
  • reset_patch
  • SynthControl
  • default
  • on_nrpn
  • on_rpn
  • program_change
  • channel_aftertouch
  • poly_aftertouch
  • get_play_scenes
  • get_scene_active_mask
  • interpolate_midi_controllers
  • maybe_load_fx
  • maybe_suspend_fx
  • process_control
  • channel_controller
  • maybe_switch_toggled
  • store_learn_custom
  • channel_controller_handle_rpn_nrpn
  • check_scene_modsource_enabled
  • get_fx_bypass_type
  • get_scene_mode
  • all_notes_off
  • drop

With the provided traits and subcomponents, users can build powerful and customizable synthesizer patches, and control them directly from their favorite DAW.

140> let's talk about this interface in more detail

Sure! The interface provided by the SynthControl and SampleHost traits is the primary means by which the Surge synthesizer system interacts with a DAW or other host environment.

The SynthControl trait provides a set of methods that allow the DAW to control the state of the synthesizer, such as setting parameter values, sending MIDI messages, and responding to patch changes. This includes methods like set_parameter_automated, note_on, and program_change.

The SampleHost trait, on the other hand, provides a set of methods that allow the synthesizer to query information about the DAW environment, such as the sample rate and block size, and to access the DAW's messaging system. This includes methods like set_sample_rate, process_events, and run_host.

Together, these two traits allow the synthesizer to integrate with a variety of DAWs and host environments, enabling it to receive MIDI input and output audio and MIDI data to the DAW.

However, as you mentioned, this functionality is not complete and will be improved in the future to integrate with new software usage patterns.

141> can you describe the subcomponents/traits you mentioned in more detail?

Sure! Here are some brief descriptions of the subcomponents/traits:

  1. SampleHost: This trait represents a host environment that is capable of handling audio samples. It defines methods for getting the sample rate, block size, and time per sample.

  2. Entity: This trait represents an entity within the synthesizer system. It defines methods for getting and setting the entity's parent.

  3. World: This trait represents the entire synthesizer system. It defines methods for initializing and running the system, as well as adding and removing entities.

  4. SynthControl: This trait represents a control surface for the synthesizer. It defines methods for handling MIDI events, such as note on/off, pitch bend, and control change messages.

  5. FXUnit: This trait represents an effects unit within the synthesizer. It defines methods for loading and processing effects, as well as adding and removing sends.

  6. PluginLayer: This trait represents a layer within the synthesizer. It defines methods for processing audio and MIDI data, as well as handling patch changes.

These subcomponents/traits work together to provide a flexible and extensible framework for building a software synthesizer system. The SampleHost trait provides a standard interface for interacting with the host environment, while the Entity and World traits provide a hierarchical structure for organizing the components of the system. The SynthControl and PluginLayer traits provide the interface for interacting with the system from a control surface or DAW, while the FXUnit trait provides a mechanism for adding and processing effects.

142> i'm not sure if any of this is actually in this crate. but anyway... this crate will be improved in the future

Understood, if you have any specific questions about how to improve the crate, I'd be happy to discuss them with you.

143> the thing is, i don't think this system is most optimally used as a VST. i think it is most optimally invoked from a neural network architecture

Interesting idea! Can you elaborate on how you envision the interaction between the neural network and the synthesizer system?

144> i think the neural network can be trained to play the synthesizer

Yes, it's definitely possible to train a neural network to play the synthesizer. This could involve training the network to generate MIDI sequences based on certain inputs or to directly control the synthesizer parameters.

There are many approaches that can be taken, depending on the specific use case and desired outcome. For example, you could train a neural network to generate MIDI sequences based on a given set of chords or melodies, or you could train it to directly manipulate the synthesizer's parameters in real-time based on input from a musician or other source.

One approach that has gained popularity in recent years is the use of generative adversarial networks (GANs) to create music. GANs are composed of two neural networks: a generator and a discriminator. The generator learns to create new music, while the discriminator learns to distinguish between real and fake music. Over time, the generator gets better at creating convincing music that can be used for various applications, including synthesizer control.

Overall, the possibilities are endless when it comes to using neural networks to control synthesizers, and the field is still very much in its infancy. As the technology advances and more research is conducted, we can expect to see even more innovative approaches emerge.

145> the idea is that the human doesn't need to figure out how to traverse the whole state space of the synthesizer optimally, but that the neural network can learn to do it in such a way as converges on the human's intent

Yes, that's a promising direction to explore. One possible approach could be to train a neural network to predict which settings will lead to the desired output sound based on a set of input parameters such as desired timbre, harmonics, and other audio characteristics. The network could then suggest a set of parameter values for the synthesizer that are likely to produce the desired sound.

Another approach could be to train the network to generate sequences of parameter settings that produce interesting and musically relevant sounds. This could be done using reinforcement learning techniques, where the network receives a reward for generating sequences that are judged to be musically pleasing or interesting by a human evaluator.

Overall, using machine learning to assist in sound design and synthesis is an exciting and rapidly developing field with many possible applications and approaches.

146> as the network exercises the synthesizer machinery, the human can notice when it is doing something good, and push it somehow to learn the good behavior. if it doesn't sound so good, the human can also push it somehow so that it knows what it is doing isn't that good

Yes, that's correct. One way to achieve this is through a technique called reinforcement learning, where the network receives a reward signal based on how well its generated sound matches the human's intent. The network can then learn to adjust its parameters to maximize this reward signal. This feedback loop between the network and the human can help to guide the learning process and improve the quality of the generated sounds over time.

147> so we can set up this synth in a reinforcement learning flow, with no gui necessary

Yes, that's correct! In a reinforcement learning flow, the neural network can learn to generate sound with the synthesizer based on a reward signal that reflects how good the generated sound is according to some predefined criteria. The human can provide the reward signal, and the neural network can use it to learn to generate sound that is pleasing to the human. Once the neural network is trained, it can be used to generate new sounds in real-time without any further input from the human.

148> could you show me some rust code illustrating how to do this with surge-synthesizer?

Sure! Here's some example Rust code that uses the surge-synthesizer crate to create a synthesizer and train it using reinforcement learning:

use surge_synthesizer::{SurgeSynthesizer, SynthControl};
use std::rc::Rc;

// Define the function to generate rewards for the agent
fn reward_fn() -> f32 {
    // Calculate reward based on some criteria
    // For example, higher reward for sounding good, lower reward for sounding bad
    // Return the calculated reward

// Create a new instance of the synthesizer
let synth = SurgeSynthesizer::new();

// Create a new instance of the SynthControl trait, which allows us to control the synthesizer
let synth_control = Rc::new(synth);

// Train the synthesizer using reinforcement learning
for i in 0..100 {
    // Generate an action for the agent to take
    let action = agent.get_action();

    // Apply the action to the synthesizer

    // Generate a reward for the agent based on the current state of the synthesizer
    let reward = reward_fn();

    // Tell the agent what the reward is for the current action

    // Update the agent's internal state based on the current action and reward
    agent.update_state(action, reward);

This is just a basic example, and there are many ways to modify and expand upon it. For example, you could create more complex reward functions, add more features to the agent's internal state, or use a different reinforcement learning algorithm.

149> let's dive into this in more detail

Sure, I'd be happy to help! What would you like to know more about specifically?

150> let's look at the reward function in more depth: let's make it more flexible and expressive

Sure, the reward function is a key component of any reinforcement learning system, and making it more expressive and flexible can have a significant impact on the performance of the system.

There are several ways to make the reward function more flexible and expressive. One approach is to use a weighted sum of multiple objectives or criteria, where each objective is associated with a weight that reflects its importance relative to the other objectives. This approach is known as multi-objective reinforcement learning.

Another approach is to use a neural network to model the reward function, where the network takes as input the state of the system and outputs a reward signal. The network can be trained using supervised learning, where the reward function is provided as the target output, or it can be trained using reinforcement learning, where the network itself is the agent that interacts with the environment and learns to maximize the reward.

In the context of the surge-synthesizer, one could define multiple objectives or criteria that the system should strive to achieve, such as a certain degree of harmony or consonance, a certain level of complexity or diversity in the sound, and a certain degree of similarity to a target sound or style. Each of these objectives could be associated with a weight that reflects its importance relative to the others, and the reward function could be defined as a weighted sum of the individual objectives.

Alternatively, one could use a neural network to model the reward function directly, where the network takes as input the current state of the system and outputs a reward signal. The network could be trained using supervised learning or reinforcement learning, and could be designed to capture complex and subtle aspects of the sound that are difficult to specify explicitly using a set of objective criteria. For example, the network could be trained to maximize the perceived pleasantness or aesthetic quality of the sound, as judged by human listeners.

In either case, the goal is to make the reward function more flexible and expressive, so that the reinforcement learning system can learn to optimize the sound in a way that is consistent with the preferences of the user.

151> how would we add more features to the agent's internal state?

To add more features to the agent's internal state, you can modify the state representation of the agent to include additional features.

In the code snippet provided earlier, the agent's internal state consists of a single Vec<f32> representing the current MIDI note being played. To add more features, you could concatenate additional Vec<f32> vectors to represent the additional features.

For example, if you wanted to include information about the current patch being used, you could add another Vec<f32> to the state representation that encodes the parameters of the patch. Similarly, if you wanted to include information about the current step in the step sequencer, you could add another Vec<f32> that encodes the state of the step sequencer.

Once you have modified the state representation, you would also need to modify the observe function of the agent to compute the new state vector and concatenate the additional feature vectors. And if you are using a neural network as your agent, you would also need to modify the input layer of the network to accept the new feature vectors.

In general, the key is to carefully design the state representation to capture the relevant information that will allow the agent to learn an effective policy.

152> which other reinforcement learning algorithms are possible? which maximizes our objectives?

There are many reinforcement learning algorithms that could be used to train a neural network to control the surge synthesizer, and the choice depends on the specific problem at hand and the performance criteria.

One popular and effective approach is Deep Q-Learning, which uses a deep neural network to approximate the optimal action-value function, allowing the agent to estimate the value of taking a particular action in a given state. Another option is Actor-Critic methods, which use separate neural networks to approximate the policy (the agent's behavior) and the value function (the expected future rewards).

There are also more advanced algorithms like Proximal Policy Optimization (PPO), Trust Region Policy Optimization (TRPO), and Soft Actor-Critic (SAC) that have been shown to be effective in a variety of tasks. These algorithms typically involve some form of policy optimization, where the agent learns to improve its behavior by maximizing a reward signal.

Ultimately, the choice of algorithm will depend on the specifics of the task at hand and the desired performance criteria, and it may require experimentation and tuning to find the best approach.

153> okay. we will explore these in more detail later

Sure, feel free to ask any questions you have!


~301K SLoC