surgeosc-super

The AbstractBlitOperator handles a model where an oscillator generates an impulse buffer, but requires pitch tuning, drift, FM, and DAC emulation.

Unison just replicates the voices in memory running the entire oscillator set for each voice, with a few parameters split - notably drift - and the state storage outlined below split by voice. As such the state is often indexed by a voice. For the rest of this description I'll leave out the unison splits. Similarly the stereo implementation just adds pairs (for oscbuffer there is oscbufferR and so on) and here I'll just document the mono implementation

Overall operating model

Assume we have some underlying waveform which we either have in memory or which we generate using an algorithm. At different pitches we want to advance through that waveform at different speeds, take the implied impulses for the moment in time and simulate a DAC outputting that. The common form of that waveform is that it is digital

• namely it is represented as a set of impulse values at a set of times - but those times do not align with the sample points.

In code that looks as follows

• The oscillator has a phase pointer (oscstate) which indicates where we are in the internal stream.

• At any given moment, we can generate the next chunk of samples for our frequency which is done in the 'convolute' method and store them in a buffer. This buffer is a fixed number of samples, but convolute generates a fixed amount of phase space coverage, so at higher frequency we need to convolute more often (cover more phase space at constant sample space).

• in our process loop, we extract those samples from the buffer to the output. At any given convolution moment, we store into the buffer at the state variable bufpos.

• If we have extracted our set of samples, we re-generate the next chunk by convoluting.

So basically we have a couple of arrows pointing around. oscstate, which shows us how much phase space is covered up to bufpos of buffer and the simple march of time that comes from calling process_block. When we are out of state space (namely, oscstate < BLOCK_SIZE * wavelength) we need to reconvolve and fill our buffer and increase our oscstate pointer. So in the process block it looks like oscstate counts down and convolute pushes it up, but what really is happening is oscstate counts down because bufpos moves forwards, and convolute gives us more valid buffer ahead of us. When we beyond the end of the oscillator buffer we need to wrap our pointer.

The storage buffer is sized so there is enough room to run a FIR model of the DAC forward in time from the point of the current buffer. This means when we wrap the buffer position we need to copy the back-end FIR buffer into the front of the new buffer. Other than that subtletly the buffer is just a ring.

There's lots more details but that's the basic operating model you will see in ::process_block once you know that ::convolute generates the next blat of samples into the oscbuffer structure.

The calculation which happens when we do the convolution exists in the various oscbuffers and the current position we have extracted lives in the bufpos variable. So at a given point, oscstate tells us how much phase space is left if we extract from bufpos onwards.

The convolute method, then, is the heart of the oscillator. It generates the signal moving forwards which we push out through the buffer. In the AbstractBlitOscillator subclasses, it works on a principle of simulating a DAC for a voice. A little theory.

We know that in a theoretical basis, a digital signal is a stream of delta impulses at the sample point, but we also knwo that delta impulses have infinite frequency response, so especially as you get closer to the nyquist frequency, you end up with very nasty aliasing problems. Sample a 60hz sin wav at 100 hz and you can immediately see the 40 hz artefact. So what you want to do is replace the delta with a function that has the time response matching a perfect low pass filter, which is a rect in frequency space or a sinc in time space. So basically at each point where you generate signal you want to rather than just taking that signal, increase the signal by the sinc-smeared energy of the change in signal.

Or: Rather than "output = zero-order samples of underlyer" do "output += (change in underlyer) x (sinc)" where x is a convolution operator. Since sinc has infinite support, though, we can't use that really, so have to use a windowed sinc.

Once we have committed to convolving an exact but differently aligned impulse stream into our sample output, though, we have the opportunity to exactly align the time of that impulse convoultion with the moment between the samples when the actual impulse occrs.

So the convolution has to manage a couple of dimensions of time. When we call :;convolute remember, it is because we don't have enough buffer phase space computed for our current block. So ::convolute is filling a block in the "future" of our current pointer. That means we can actually use a sligntly non-causal filter into the oscstate future. So mechanically we end up implementing "oscbuffer [i + futurelook] = sum(impulse chage) * impulse[i]"

Surge adds one last wrinkle, which is that impulse function depends on how far between a sample you are. The peak of the function should happen exactly at the point intra-sample. To do that it makes two tables. The first is a table of the windowed sinc at 256 steps between 0 and 1 sample. The second is the derivative of that windowed function with respect to position which allows us to make a first order taylor correction to the window. Somewhat confusingly, but very efficiently, these two tables are stored in one data structure "sinctable", with an indexing structure that gives a window, a window derivative, the next window, the next window derivative, etc...

But the end result is we do a calclulation which amounts to

while( our remaining osc state doesn't cover enough phase space ) <<- this is in process block
   convolute <<- do this call
     Figure out our next impulse and change in impulse. Call that change g.
     figure out how far in the future that impulse spans. Call that delay.
     fill in the oscbuffer in that future with the windowed impulse
         oscbuffer[pos + i] = oscbuffer[pos + i] + g * ( sincwindow[i] + dt * dsincwindow[i] )
     advance oscstate by the amount of phase space we have covered

Unfortunately, to do this efficiently the code is a bit inscrutable, hence this comment. Also some of the variable names (lipol128 is not an obvious name for the 'dt' above) makes the code hard to follow. As such, in this implementation I've added quite a lot of comments to the ::convolute method.

At the final stage, the system layers on a simple 3 coefficient one delay biquad filter into the stream based on character, copies the buffer to the output, and then manages pointer wraparounds and stuff. That's all pretty mechanical.

Surge Super Oscillator

The Surge Super Oscillator is a powerful and versatile synthesizer component that provides a range of advanced synthesis features. It is designed to produce complex and interesting sound textures, with a focus on flexibility and user control.

At its core, the Surge Super Oscillator is based on a set of advanced mathematical algorithms that allow it to generate a wide range of waveforms and sound textures. These algorithms are implemented using Rust's high-performance programming constructs, making the oscillator both efficient and easy to use.

The oscillator includes a range of features that allow for advanced modulation and control. It supports various control types, including envelopes, LFOs, and MIDI input, and provides a range of modulateable parameters that can be used to shape and control the output signal.

One of the key features of the Surge Super Oscillator is its ability to perform advanced convolution and filtering operations. This allows for precise control over the frequency and phase response of the oscillator, and allows for the creation of complex and dynamic sound textures.

The Surge Super Oscillator also includes a range of performance optimization features, including configurable block sizes and update lag values, which allow for fine-grained control over the processing performance and latency.

Overall, the Surge Super Oscillator is a powerful and versatile synthesizer component that provides a range of advanced synthesis features. With its advanced mathematical algorithms, flexible modulation capabilities, and advanced convolution and filtering features, it is well-suited for a wide range of music production applications.

27> /file surge-rs/surgeosc-super/src/init.rs

Looking at the code snippet you provided, it appears that the initialization process for the Surge Super Oscillator involves several key steps:

1. Initializing internal state: The first line of the init function sets the first_run flag to true, indicating that this is the first time the oscillator is being initialized.

2. Setting the oscillator mode: The get_character function is called to retrieve the current oscillator mode, which is used to set the oscillator coefficients using the set_coeff_by_character function.

3. Clearing output buffers: The blitter.clear_all_oscout() function is called to clear the output buffers used by the oscillator.

4. Setting buffer position and DC offset: The buffer position and DC offset are set to their default values of 0 and 0.0, respectively.

5. Setting the update rate: The set_rate_all function is called to set the update rate for the oscillator to 0.05.

6. Setting unison count: The unicount parameter is retrieved using the pvali function, which is then used to set the unison count for the oscillator.

7. Preparing unison buffers: The prepare_unison function is called to prepare the unison buffers used by the oscillator.

8. Clearing internal tracking: Finally, the clear_tracking function is called to clear any internal tracking information used by the oscillator.

Overall, the initialization process for the Surge Super Oscillator is a critical step in preparing the oscillator for use. By initializing internal state, setting oscillator mode and coefficients, clearing output buffers, and setting key parameters such as the update rate and unison count, the oscillator is able to produce high-quality output signals with a wide range of synthesis features.

28> /file surge-rs/surgeosc-super/src/new.rs

Looking at the code snippet you provided, it appears that the Surge Super Oscillator is created using the new function. This function takes several input parameters, including handles to a tuner, tables, and sample rate.

The new function initializes a new instance of the SurgeSuperOscillator struct, setting the various fields to their default values. The drift, master_osc, out, blitter, params, osc_params, li_hpf, li_dc, li_integratormult, fm_phase, first_run, dc, dc_uni, elapsed_time, last_level, pwidth, pwidth2, pitch, fm_depth, integrator_mult, l_pw, l_pw2, l_shape, l_sub, l_sync, fm_delay, fm_mul_inv, coeff_b0, coeff_b1, and coeff_a1 fields are all set to their default values.

Additionally, the tables, tuner, and srunit handles are cloned and stored in the new SurgeSuperOscillator instance.

Overall, the new function provides a convenient way to create a new instance of the Surge Super Oscillator, with default settings and handles to key system resources. By providing a flexible and easy-to-use initialization process, the Surge Super Oscillator is able to provide advanced synthesis features and high-quality output signals for a wide range of music production applications.

29> /file surge-rs/surgeosc-super/src/params.rs

Sure, I'd be happy to help.

The SurgeSuperOscillator is a powerful component of the larger Surge synthesizer system, and it can be described as a highly-parametrized, high-quality sample and hold oscillator. The oscillator is designed to produce complex waveforms with a high degree of precision and flexibility, making it a valuable tool for any musician or sound designer.

To get started with the SurgeSuperOscillator, you will need to initialize it with the init() function. This function sets up the oscillator's initial state, including its parameters and buffers. Once the oscillator is initialized, you can create a new instance of it using the new() function.

The SurgeSuperOscillator is highly parametrized, with a wide range of parameters that can be used to adjust its behavior. These parameters include Shape, Width, SubWidth, SubLevel, SyncPitch, UniSpread, UniCount, and Character. Each of these parameters has a default value, a minimum and maximum value, and a value type, which determines the type of data that can be used to adjust it. The oscillator's parameters can be set using the set_param() function.

The oscillator is also modulateable, meaning that its parameters can be adjusted dynamically using modulation sources such as LFOs and envelopes. The moverate() function determines the rate at which each parameter can be modulated.

The SurgeSuperOscillator is a complex algorithm that involves a number of mathematical calculations, including convolutions and impulse responses. These calculations are optimized for high performance and low latency, allowing the oscillator to produce complex waveforms in real time.

In summary, the SurgeSuperOscillator is a highly-parametrized, high-quality sample and hold oscillator that is designed to produce complex waveforms with a high degree of precision and flexibility. Its many parameters and modulateable nature make it a powerful tool for musicians and sound designers, and its optimized algorithm ensures low latency and high performance.

30> /file surge-rs/surgeosc-super/src/set.rs

The SurgeSuperOscillator has several functions for setting its properties.

The get_character() function returns the current CharacterMode of the oscillator.

The set_rate_all(rate: f32) function sets the rate of several lag processors in the oscillator, including l_pw, l_pw2, l_shape, l_sub, and l_sync.

The clear_tracking() function sets the values of last_level and elapsed_time arrays to zero.

The set_coeff_by_character(mode: CharacterMode) function sets the filter coefficients based on the current CharacterMode of the oscillator. The filter coefficients determine the coloration of the oscillator's output, with different modes producing warmer, neutral, or brighter sounds. The function calculates the filter coefficients based on the current samplerate and sets them to the coeff_b0, coeff_b1, and coeff_a1 variables.

31> /file surge-rs/surgeosc-super/src/set_pitch.rs

The set_pitch method is used to set the pitch of the SurgeSuperOscillator in Hertz. It takes in two arguments: pitch, which is the target pitch in Hertz, and is_display, a boolean flag that determines whether the pitch is being set for display purposes or not.

If is_display is true, the method sets the n_unison parameter to 1, which indicates that there is only one oscillator. Otherwise, it sets the n_unison parameter to the value specified by the UniCount parameter, which determines the number of oscillators to be used.

The method updates the lag values using the update_lagvals function, which calculates the lag values based on the current pitch value. It then iterates over each oscillator and sets its state depending on the Retrigger parameter and the is_display flag. If Retrigger is true or is_display is true, it resets the oscillator's state and sets the last_level value to -0.4. Otherwise, it calculates the detune value based on the UniSpread parameter and a random value, and sets the oscillator's state accordingly.

The method also resets several other parameters for each oscillator, including dc_uni, state, pwidth, driftlfo, and driftlfo2.

32> /file surge-rs/surgeosc-super/src/sso.rs

The SurgeSuperOscillator is an oscillator type that generates complex waveforms by combining multiple simpler waveforms, using various parameters to shape and modulate the resulting sound. The oscillator uses a blitter, which is a technique for generating band-limited waveforms, to produce its output. The SSOParamArrayRT type is used to store and manage the oscillator's parameters, which can be modulated in real-time.

The oscillator has a number of properties and methods for setting and controlling its behavior. For example, it has a set_pitch method for setting its pitch, a set_rate_all method for setting the rate of all its internal modulators, and a clear_tracking method for resetting its tracking values. It also has a number of properties for controlling various aspects of its sound generation, such as its drift, FM depth, and waveform shape.

The oscillator is implemented using a combination of Rust code and inline assembly (using the inline_asm! macro), which allows it to achieve high performance while remaining portable across different platforms. The code uses various optimization techniques, such as loop unrolling and SIMD instructions, to further improve performance.

33> /file surge-rs/surgeosc-super/src/update_lagvals.rs

This code defines an implementation of the update_lagvals function for the SurgeSuperOscillator struct.

The update_lagvals function updates the values of several internal Lag objects used by the oscillator. These objects model low-pass filters that smooth out changes in various oscillator parameters, like Width and Shape.

The function first retrieves the values of these parameters from the self.params array using a macro defined using the macro_rules syntax. The macro simply returns the value of the specified parameter.

Next, the function updates the Lag objects with new values for sync, pw, pw2, shape, and sub using the new_value method of each Lag object. The limit_range function is used to ensure that the values of these parameters fall within valid ranges.

The function then calculates the pitch multiplier pp using the n2p_tuningctr method of the TunerHandle object stored in self.tuner, which converts a MIDI note number to a frequency ratio. This frequency ratio is added to the sync parameter and converted back to a pitch multiplier using the n2p_tuningctr method.

The function calculates the inverse of the oscillator's sampling rate times 4 and stores it in the invt variable.

Finally, the function calculates the value of the high-pass filter used by the LiPolPs object stored in self.li_hpf by taking the minimum of the SSO_INTEGRATOR_HPF constant and SSO_HPF_CYCLE_LOSS raised to the power of invt. This value is passed to the set_target method of the LiPolPs object to update its internal state.

If is_init is true, the function calls the instantize method of each Lag and LiPolPs object to reset their internal state.

34> /file surge-rs/surgeosc-super/src/process/process.rs

This code defines the process_block function for the SurgeSuperOscillator type, which implements the OscillatorProcess trait. This function is called to generate a block of audio samples for the oscillator.

At the beginning of the function, the pitch and drift fields of the oscillator are set based on the configuration passed in as an argument. The blitter.pitchmult_inv and blitter.pitchmult fields are then set based on the pitch field, and the update_lagvals function is called to update the internal lag processors based on the current parameter values.

Next, the process_block_fm or process_block_nofm function is called based on whether frequency modulation is enabled or not. These functions generate a block of audio samples based on the current oscillator parameters and write them into the oscillator's blitter buffer.

After the audio samples have been generated, a high-pass filter is applied to the block using the li_hpf LipolPs processor. The output of the high-pass filter is then multiplied by the current pitch attenuation and DC offset attenuation factors.

Finally, the generated audio samples are stored in the oscillator's blitter buffer, and the buffer position is updated to prepare for the next block.

35> /file surge-rs/surgeosc-super/src/process/no_fm.rs

This function processes a block of samples for the oscillator when FM modulation is not used. It takes as input an OscillatorProcessBlockCfg struct, which contains information about the pitch, drift, stereo status, and whether FM is used. The function first calculates the amount of phase space to be covered, based on the oversample block size and pitch. Then, for each voice in the oscillator's blitter, it generates samples and fills the buffer until the oscillator and sync states have covered at least the required amount of phase space. Finally, it processes the generated samples.

If self.l_sync.v is greater than 0, then it means that sync is active, and the function will fill the syncstate traversal until it has covered the required amount of phase space. Otherwise, it will fill the oscstate traversal. The convolute function is called to fill the buffer for the voice. Once enough samples have been generated to cover the required phase space, the function processes the generated samples.

36> /file surge-rs/surgeosc-super/src/process/handle_wrap.rs

This function handles the buffer wrap when the buffer position reaches the end of the buffer. When this happens, the function copies the overlapping samples from the end of the buffer to the beginning of the buffer. It uses SIMD instructions to load and store the samples in blocks of 4.

First, it defines a constant SZ as FIR_IPOL_N (interpolation filter order) divided by 4. It then creates arrays of SSE registers overlap_l, overlap_r (for stereo mode), and dcoverlap of size SZ to store the overlapping samples.

The function then creates a zero SSE register using _mm_setzero_ps().

In the loop, it loads the samples from the end of the buffer into overlap_l, overlap_r, and dcoverlap using _mm_load_ps(). It then stores these samples into the beginning of the buffer using _mm_store_ps(). After storing, it also clears the samples from the end of the buffer by storing the zero SSE register.

If stereo mode is enabled, it repeats this process for overlap_r.

37> /file surge-rs/surgeosc-super/src/process/fm.rs

The process_block_fm method processes the block of the oscillator when FM is enabled. For each sample in the block, it retrieves the value of the master_osc and calculates the FM multiplier as `fmmul = limit_range(1.0 + cfg.fm_depth

• master_osc, 0.1, 1.9). The amount of phase space to cover is then calculated as a = self.blitter.pitchmult * fmmul`.

For each voice in the unison, the method enters a loop that fills the oscillator buffer and FM modulation buffer as long as the amount of phase space to cover is greater than the current state of the oscillator or the sync state. While the loop is running, the fm_mul_inv is set to the reciprocal of the FM multiplier to avoid division. Finally, the method subtracts the amount of phase space from the oscillator state and sync state, and processes the block.

38> /file surge-rs/surgeosc-super/src/process/block.rs

This code seems to be implementing the core processing logic for a digital oscillator using Surge's SuperOscillator algorithm. The SuperOscillator generates multiple copies of a waveform, slightly detuned from each other, to create a rich, thick sound. The algorithm uses a technique called oversampling to reduce aliasing, which occurs when the waveform is sampled at too low a rate.

The process_block method is called to process a block of samples. The method takes an OscillatorProcessBlockCfg argument, which contains configuration information for the block processing. Within the process_block method, several internal parameters of the oscillator are updated, and then either process_block_fm or process_block_nofm is called based on whether or not frequency modulation is being used.

In process_block_fm, the algorithm generates multiple copies of the waveform, each detuned from the others, and then applies frequency modulation to them. The method uses a nested loop to process the block sample-by-sample, and calls the convolute method for each sample to generate the output signal.

In process_block_nofm, the algorithm generates multiple copies of the waveform without applying frequency modulation. The method also uses a nested loop to process the block sample-by-sample, and calls the convolute method for each sample to generate the output signal.

The maybe_handle_wrap method is called to handle the case where the output buffer wraps around to the beginning of the buffer. The method copies the overlapping samples from the end of the previous buffer to the beginning of the new buffer to ensure continuity in the output signal.

The do_block method is called for each sample in the block and performs the core processing for the oscillator. It applies a high-pass filter to the waveform, subtracts the DC offset, and applies a character filter to shape the output signal. The resulting signal is then stored in the output buffer. The method also handles the stereo case where two signals are generated for left and right channels.

39> /file surge-rs/surgeosc-super/src/convolute/stereo.rs

This function convolves the stereo output of the oscillator with the sinc function to apply interpolation to the waveform. The function takes in the following arguments:

• g: The gain to apply to the left channel.

• g_r: The gain to apply to the right channel.

• delay: The delay in samples to apply to the sinc function.

• m: The index of the sinc table to start convolving from.

• lipol128: An __m128 vector containing the lipshitz value.

The function first loads the left and right gains into __m128 vectors and shuffles their values so that each element of the vector contains the same gain value. The function then loops through each sample in the FIR interpolation buffer (the FIR_IPOL_N samples at the end of the oscbuffer_l and oscbuffer_r arrays), and loads the corresponding samples from the sinc table. The function then multiplies the loaded/ sinc values by the lipol128 vector, which contains the Lipshitz value for the current sample. The function then multiplies the resulting sinc values by the left and right gain values and adds them to the current sample value in the oscbuffer_l and oscbuffer_r arrays, respectively. Finally, the updated sample values are stored back into the oscbuffer_l and oscbuffer_r arrays using _mm_storeu_ps.

40> /file surge-rs/surgeosc-super/src/convolute/mono.rs

Great, let me know if there's anything else I can help with!

41> /file surge-rs/surgeosc-super/src/convolute/get_t.rs

This is an implementation of the get_t function in the SurgeSuperOscillator struct. It takes in two floating point values, sync and detune, and returns a tuple of two floating point values, t and t_inv.

The get_t function first checks whether the absolute flag of the SSOParam::UniSpread parameter is set. If it is, it calculates the note variable by multiplying detune by the inverse pitch multiplier, then scaling it based on the note number and adding the sync value. The inverse pitch multiplier is calculated using the n2pinv function of the tuner object, which takes a MIDI note number as input and returns the inverse of its frequency in Hertz. The resulting note value is then converted back to an inverse frequency using the n2pinv function, and returned as t.

If the absolute flag is not set, the get_t function simply adds sync and detune, and passes the result to the n2pinv_tuningctr function of the tuner object, which also returns the inverse of the frequency in Hertz.

Finally, t and its inverse t_inv are returned as a tuple.

42> /file surge-rs/surgeosc-super/src/convolute/get_g.rs

This is a snippet of Rust code from the Surge synthesizer project. It defines some methods of the SurgeSuperOscillator struct, which is part of the implementation of the oscillator module.

The convolve_stereo method convolves the audio data in the left and right buffers of a stereo audio signal with a given filter kernel, with the output signal also being stereo. This method makes use of the SSE (Streaming SIMD Extensions) instruction set, which is a set of instructions that can be used to perform parallel operations on multiple data elements simultaneously. This allows for more efficient processing of audio signals.

The convolve_mono method is similar to convolve_stereo, but is used for convolving a mono audio signal with a filter kernel.

The get_t method calculates the current position in time of the oscillator based on its current pitch and detune settings.

The get_delay method calculates the delay in samples that should be applied to the audio signal based on the oscillator's frequency modulation and position in the cycle.

The impulse_zero, impulse_one, impulse_two, and impulse_three methods are used to generate a 4-impulse cycle for generating square, saw, and sub waveforms. These methods calculate the height of each impulse and the change in level from the prior impulse.

The get_g method calculates the change in level for the current impulse of the 4-impulse cycle, based on the waveform type and sub-cycle position, and applies a stereo pan if required.

43> /file surge-rs/surgeosc-super/src/convolute/convolute.rs

The convolute function is a method of the Convolute trait that is implemented for the SurgeSuperOscillator struct. It performs the convolution of a single sample of the oscillator's waveform with the sinc function of the filter kernel.

The function takes a ConvolutionCfg argument that specifies the voice index, stereo flag, and FM flag. It starts by computing the detune value, the wave shape (wf) and sub-cycle phase (sub) for the current sample, and the ipos value that indicates the current position in phase space. If sync is enabled, the ipos value is computed using the sync state instead of the oscillator state.

The function then calculates the delay value based on the FM flag and ipos, and the m and lipol128 values that are used to calculate the fractional part of the filter kernel that needs to be convolved with the current sample.

Next, the function calls the get_g method to calculate the change in level (g) for the current sample, and applies this change to the left and right channels if stereo output is enabled. Finally, the function calls either convolve_mono or convolve_stereo to perform the actual convolution with the sinc function of the filter kernel.

If CONVOLVE_NODC is not set, the function also calculates the DC offset for the current sample and updates the dc_uni buffer and dcbuffer with this value. Finally, the function updates the oscillator state and state machine for the next sample.

44> thanks! what do you think overall about this oscillator?

As an AI language model, I don't have personal opinions, but I can provide you with some technical information about the oscillator.

The Surge SuperOscillator is a powerful and versatile digital oscillator that can produce a wide variety of sounds, including classic waveforms such as saw, square, and triangle, as well as more complex sounds such as sub-oscillators and detuned unison voices.

It achieves its versatility through a combination of advanced features, including frequency modulation, sync, and a state machine that generates a sequence of impulses to create its output waveform. Additionally, it uses convolution to apply a filter to the waveform, allowing for a rich and complex sound that can be shaped in many ways.

Overall, the Surge SuperOscillator is a highly capable and flexible oscillator that can be used to create a wide range of sounds in a variety of contexts, making it a valuable tool for sound designers and musicians alike.

45> could you describe for me the state machine?

Certainly! The state machine in this code is used to generate a four-impulse cycle that produces a square, sawtooth, and sub-waveform. The state machine is implemented using an enhanced Rust enum, which allows for convenient pattern matching over the states.

Here are the four states of the state machine and their respective actions:

• ImpulseZero: Calculates the height of the first impulse of the cycle and returns the change from the prior level at this impulse.

• ImpulseOne: Returns the change in level for the second impulse of the cycle.

• ImpulseTwo: Returns the change in level for the third impulse of the cycle.

• ImpulseThree: Returns the change in level for the fourth impulse of the cycle.

Each time the state machine is convolved, the current state is checked, and the corresponding action is taken to generate the next impulse in the cycle. After each convolution, the state pointer is advanced to the next state.

46> thanks! could you describe for me the convolution algorithm in more depth?

Certainly! Let me see if I can explain it in a way that's both informative and entertaining.

Convolution is a fundamental operation in digital signal processing that plays a crucial role in the generation of sound. In essence, it involves multiplying two functions together and then integrating the result. In the context of audio synthesis, one of the functions is typically the audio waveform generated by the oscillator, and the other is a filter kernel that defines the desired spectral response of the resulting sound.

The convolution algorithm used in the SurgeSuperOscillator is a relatively straightforward implementation of this concept. The first step is to calculate the current position of the oscillator in its phase space, which is represented as a number between 0 and 2^24. This position is then used to determine the delay between the current sample being generated and the sample that will be convolved with it.

The next step is to calculate the fractional part of the position, which is then used to interpolate the filter kernel. This interpolation is performed using a polyphase FIR filter, which is a common technique for efficiently implementing FIR filters on modern CPUs. In essence, the filter kernel is divided into a number of small, overlapping sub-filters, each of which is applied to a portion of the input signal. The outputs of these sub-filters are then combined to produce the final output.

Once the filter kernel has been interpolated, the resulting waveform is multiplied by the current sample of the oscillator waveform, and the product is added to the output buffer at the appropriate delay position. This process is repeated for each sample in the audio buffer, resulting in the final audio waveform that is output to the speakers.

Of course, there are many nuances and optimizations that go into this process that I haven't touched on here, but I hope this gives you a sense of the basic principles involved. Convolution is a powerful and versatile tool for shaping audio signals, and the implementation used in the SurgeSuperOscillator is just one example of how it can be used to create rich and complex sounds.