In this comprehensive tutorial we will cover various methods of Cricket Chirp synthesis, and the three stages leading to the Hybrid Synthesis Cricket Chirp Tool (CCT): Background theory, Analysis and Synth Techniques.
While we will touch on other great synthesizers like Alchemy (now owned by Apple) and Massive, we will mainly explore Absynth 5 while using iZotope Insight and iZotope RX 3 for analysis. This post is complementary to my Cricket Synthesis video and series.
The result of applying these techniques with a versatile synth like Absynth is a hybrid synthesis that's capable of producing a wide range of common aesthetics. Before we conclude with the CTT, lets look at some background and explore the different synth techniques and their advantages.
Background
Fig.1 - Stridulation rasp of the grasshopper
Image courtesy of Gilles San Martin (Own work) (https://www.flickr.com/photos/sanmartin/4815245982/)
The sound produced by crickets is often the result of stridulation, which is the vibration of the forewings against each other. There is a series of teeth underneath the upper wing (Fig.1) that are rubbed against the plectrum of the other wing. These are amplified additionally by the wing vibration itself.
One chirp syllable is the sound of one open and close of the forewings!
It has been interesting to note the vast range of sounds that we can perceive as cricket chirps.
Flexibility
There's a few factors that allow for flexibility of chirps in sound design:
- There are over 900 species of crickets on the planet, which offers our ears a great variety of sounds!
- They're often heard at a distance from the source, not usually close proximity, giving some leeway for how much detail we need. The frequency dampening is predictable and the chirp reverberates in the environment.
- They are relatively simple, being at a set frequency of;
- a constant chirp rate, or
- groups of chirp syllables with pauses.
Analysis
My own recordings of Cricket chirp environments revealed that there were quite a variety to choose from, but there were still some predictable, familiar properties.
While there are many patterns and rhythms of different chirps, the two common styles were the House Cricket (high pitch, syllable triplet rhythms) and a Mole Cricket type (raspy lower frequency, humming). The first is made up of a cluster of harmonics in a narrow frequency range (Fig.2), and the second, more challenging type has only a few distinct harmonics (Fig.3).
I sought these two recordings below on Avisoft Bioacoustics, which is a prime resource for audio recordings and spectra of various species. It is a must visit for anyone interested in researching sounds of wildlife and insects. I also had a quick look through this paper called Bioacoustics of the Neotropical Eneopterinae, which provided some great info.
Fig.2 - Spectrum Analysis of Mole Cricket
Fig.3 - Spectrum Analysis of House Cricket
Although many of these insects communicate ultrasonically, exceeding 20khz - 100khz, the main audible range is typically from 2 and 8 khz. The fundamental resonance shown for the House Cricket in Fig.3 is about 4.9khz, whereas the Mole Cricket in Fig.2 and Fig.4. below is about 2.2khz. The graph below will also be useful to refer to later in the article.
Fig.4 - The above spectrum of the Mole Cricket (edited from video) displays a cluster of frequencies at the anchor point. With a FFT Window size of 1024 samples, it includes 1 - 2 chirp syllables and displays a reasonable analysis. While this method of numbering harmonics is true in general, the Rate of 42.8hz also correlates to the Sample Rate divided by FFT Window.
Synth Techniques
This section will detail from the more accessible techniques to advanced ones. The main focus is to create a cluster of harmonics as shown in Fig.4.
- Ring Modulation (Ringmod)
- FM Synthesis (Frequency Modulation)
- Customized Envelopes (secondary technique)
- Additive Synthesis
- Filter Modulation (secondary technique)
In all cases, ensure you have a steep Attack and steep Release envelope, as we are dealing with fast chirping. Generally, the Sustain level of the envelope can be kept at 100%, while the modulation can come later.
The humming may be achieved with a static tone at a set frequency, whereas the syllable chirps can also be made with a second amp modulation:
- Pulse wave LFO (including customised LFO shape - as mentioned in the last section);
- Ramped envelopes with pauses;
- A Granular synth engine (e.g. shallow stream with gaps).
Ring Modulation (Ringmod)
One of the easiest methods to produce a narrow band frequency 'buzz' is with Ring Modulation. Most synthesizers with Ringmod will default to a Sine wave modulator, which will produce 2 multiple of the carrier waveform - resulting in the sum and difference partials on either side of the carrier frequency. When these frequencies are close together, around 35hz, the sound buzzes, due to the narrow stimulation of our inner ears 'critical band'. If you're fortunate to choose the modulator waveform like you can in Absynth, choose a Triangle wave for a soft but richer range of sidebands.
Fig.5 - The patch is a sine wave ring-modulated with a Triangle. Using this wave as a modulator will create a wider series without sounding rough like a Saw wave, or plain like a Sine wave.
Fig.6 - The Waveshape Module adds a non-linear brightness to the cluster.
Set the Osc carrier frequency to 2khz, and the modulator to about 35hz difference (Fig.5). The first two sidebands on either side will then equal 1965hz | 2035hz. When using modulation, I found that high frequencies can sound good up to around 70hz, while lower ones create more buzz. The lower the mod frequency, the lower the difference from the carrier frequency.
Since the carrier wave is preferred to be a single sine wave, whether it is mixed in or out is not essential, but keeping it mixed in will also result in slightly more buzz.
The wave shaper (Fig.6), which I often use, is to brighten the sound by adding extra octave harmonics above the fundamental - this almost duplicates the whole spectrum upwards. It seemed to be a common observation that there are upper harmonic clusters, although quieter.
Using Ringmod in this way creates a simple group of harmonics that is more authentic than a single frequency, which on its own does not 'buzz.' At best, a single frequency may sound acceptable to our perception of crickets only at great distances, where the buzzing effect begins to drop off.
Lastly, modulate the Osc's amplitude with a Pulse-wave LFO (33% Width), and adjust the rate for a good chirp rhythm.
FM Synthesis (Frequency Modulation, Phase Mod)
A powerful way to add rich side bands is with Frequency Modulation. Modulating the carrier waves' frequency with that of another oscillator module is a way to increase the amount of sidebands, the main parameters being the FM Index and Mod Frequency.
Fig.7 - Increasing the Phase Mod Amount (FM Index) in Massive
Fig.8 - Increasing Fm Index in Absynth
Using a low Mod Frequency (35-70hz) keeps the Sidebands close together. This is when Absynth's Oscillator Hz legend comes in handy. If you don't have it on your synth, try tuning the modulator in the lower 3 Octaves (0 - 2). The above images show both methods of this: E.g. D1 of 36.7hz (as modulator, Fig.8), is transposed about -60 semitones below C7 of 2093hz (as carrier, Fig.7).
In Fig.8, I have the sine wave close to 2khz, and the modulator at about 70hz. The FM Index is 3 and up. Increasing the FM Index is like ramping up the FM depth - it increases the number of sidebands. The chirp period is created with a pulse-wave LFO shape, with about 1/3rd width.
This was favourable for the mole cricket, cicadas and other raspy insect sounds that have heavier vibration sounds. It is the wide frequency cluster that contributes to the 'heaviness'. Not to mention that cicadas can be extremely loud!
Additive Synthesis (Virtual Analog, Wavetable Synthesis)
The first example of Additive synthesis is probably the easiest of all; creating a mild buzz sound with only two frequencies, or Sine oscillators. You can try three if you have 3 Sines, but other methods like Ringmod are still preferable and easier to attempt.
Fig.9 - Using only 2 Sine wave Oscillators in Alchemy; one Osc has tuning offset.
The next example relies on an Additive engine where individual harmonics can be mixed. Both Absynth 5 and Alchemy can have customised partials. Xfer Record's Serum is another powerhouse synth capable of detailed additive wavetables.
Fig.10 - Drawing a cluster of Harmonics in Absynth's Wave Editor
Fig.11 - Analysing the main 11 Harmonics with high zoom.
The above buzzing sound was made with an Additive oscillator, starting with a basic cluster of 11 harmonics, with a fundamental of 63hz. Displayed above in Fig.10-11, this example was a pretty acceptable estimate of the spectrum shown earlier in Fig.4 - which is simplified again with the FFT formula (1024 FFT = 42.8hz window).
Importing a sample chirp into Absynth lets us look closer at the spectrum in the Wave Editor (Fig.12). Absynth's spectrum in the bottom-right displays the first 64 harmonics. You can see that the spectrum has a cluster that is more elaborate, but similar to what we produced above. The advantage of this import is that that we have the precise waveshape; the Phase of each harmonic is preserved. Knowing that every harmonic has its own phase also helps us understand the 'silence' in the second half of the wave.
Fig.12 - Using Absynth's 'Import from Audio File' Transform function, a sample of the Mole Cricket chirp confirms the frequency cluster (44.1khz resampled). This is used as a fixed frequency oscillator in Absynth at 42.8hz. You can see the Phase information for each harmonic is preserved to give an accurate Waveform. Variation to the chirp over time can easily be added with LFOs. See the Microsounds video.
Customized Envelopes (Secondary Technique)
A more distinct example is the House cricket, which has the first four harmonics intact, but needed a custom envelope built for the distinct chirp syllables. Here there are ramp envelopes for 3 syllables and a pause. That equals about 17 syllables a second. The pitch is also enveloped to fluctuate rapidly, but only slightly.
A much easier way to use repetitive envelopes is to use the synced Performer in NI Massive, or attempt a custom LFO shape with a pause (see Hybrid Synthesis section).
Fig.13 - Using tiny envelopes in NI Absynth's Envelope window. The Osc now has only 4 Harmonics and a bright Waveshaper. Not the easiest, but still doable.
Filter Modulation (Secondary Technique)
Fig.14 - Adding a Bandpass Filter for a spike.
Alchemy's Mole cricket example here (FIg.14) contains a similar cluster to that of Absynth's in FIg.10-11, but also has a steep Bandpass filter applied for a fundamental resonance. Slightly varying the cutoff frequency gives a rather natural fluctuation to the humming, without changing the Osc frequency. Mysteriously, the resonance is not actually that predominant in the recording, but it sounds very acceptable.
Interestingly, varying the cutoff frequency rapidly, at an irregular rate (Noise shape, see Fig.15) creates a cloudy, organic sound. If it is fast enough, the sound appears to be reverberating. Modulating the cutoff frequency is a great way to create movement and variation within the static bed of harmonics.
Fig.15 - Modulating the Bandpass Filter Freq (cutoff) in Absynth, with a Noise 1 LFO creates a cloudy, organic sound.
Hybrid Synthesis
Here is the most advanced 'method' of synthesis - a semi-modular combination of different synthesis methods. So far, a single oscillator has achieved a lot. But in the Cricket Chirp Tool project, the 3 Osc modules of Absynth were used for even further variation.
A sneak peak of the Patch Window and Main Chirp shape is shown in Fig.16. A meter-tapped demo, illustrating the 3 oscs in the video is below-right.
Fig.16 - Main view of the Cricket Chirp Tool, which combines 3 different Oscilators, Custom LFO Shapes and Delay FX.
This video demo's a spectrogram of each the 3 oscillators and their impact on the timbre.
The main features of this hybrid approach include the ability to combine:
- FM Synthesis Osc - for rasp, growl
- Ringmod Osc - for pure tone, simple buzz
- Wavetable Osc - (Noisy type) for a plastic flutter, presence, buzz of 'wing' sound. While the first 2 Oscs are tuned the same, Osc 3 retains different tunings to occupy the middle and brighter part of the spectrum.
In addition, Absynth's architecture allowed for:
- Custom, Morph Wave LFO Shapes - for dynamic, versatile LFO shapes that can retain syllables at low or high rates. The shape and depth are also tweakable between monotonous buzzes and chirp patterns.
- Granular FX - for reverberation and delay FX, creating immense 'chorus' effects.
Most impressively, the CCT Macro Controls can be assigned to the above parameters, and others, to create a cricket chirp instrument! Even the ability to simply mix in and out between 3 different Oscs can create a vast range of timbres. The Cricket Chirp Tool has 14 Macro Controls assigned.
To download the super patch itself, sign up here. It's free.
I hope you have enjoyed this article and found it practical. As you can see, each synthesis method has a different approach to the target spectrums, or at least sounding usable. Cricket chirps are easier to create and more accessible than I thought. Analysing the spectrum, even on this tiny scale, provides a very practical target to aim for. Remember, the technique you prefer will depend on the quality and creativity you're looking for.