Tag Archives: synthesis

Synthesising the THX Deep Note with Max and MC objects

The addition of MC to Max 8 added some handy ways to organise audio signals. One of the simplest benefits is the ability to pack stereo channels together with mc.pack~ 2 and process each of the channels with only half of the number of objects taking up space in your patcher (filtering stereo signals would previously require multiple biquad~ objects for example). MC also opens up some helpful ways to think about additive synthesis voices, richness of sound, and polyphony, and simplifies the patching needed to realise certain kinds of synthesised sounds.

One thing that is really wonderful about MC is the simplicity in which synthesised sounds can be made richer and fuller in the stereo space by modifying a group of oscillators’ frequencies and panning the individual ‘voices’.

Many softsynths — such as Native Instruments’ FM-8 — offer the ability to add more voices to ‘fatten up’ a sound.  The addition of extra oscillators combined with a small amount of detune adds a fullness to the sound that — before MC came along — would have required a fair amount of patching to replicate in Max. With MC objects though, this can be accomplished quite simply with MC object messages like ‘deviate’ and ‘spread’ eg. deviate 0.1 0 (to produce random bias values ranging between -0.1 to 0.1 for each voice of an oscillator) and spread 0. 1. (sent to the right inlet of mc.phasor~ to evenly spread the phase of a series of control oscillators, for example). Using these messages with objects like mc.sig~ can be useful ways to widen MC signals within the stereo space when mixing them to stereo with mc.stereo~ (or mc.mixdown~ 2).

Synthesising THX Deep Note using MC

Several years ago, on the 35th anniversary of its first screening, THX Ltd. released James A. Moorer’s score for the ‘THX Logo Theme’. Commonly referred to as the THX ‘Deep Note’ the theme is an instantly recognisable musical motif of swirling noise that coalesces into a D Major chord spanning 5 octaves.

The score describes the THX Logo Theme as thirty voices at random pitches between 200Hz and 400Hz.  Each voice moves slowly and randomly for a short time before proceeding to a predefined target note. The idea lends itself beautifully to MC. [Source: https://www.facebook.com/thxltd/photos/a.379994786929/10155235575876930/]

Building the THX Deep Note in Max is a great conceptual exercise, and drawing on the MC approach of thinking makes producing something like this quite straightforward. Here’s an example of how it might be done.

How does the patch work?

  1. An mc.sig~ object is given 30 voices all of MIDI pitch 61 (or C#3).
  2. These are scaled to the range 55–67 by an mc.rand~ object that outputs 30 randomly varying values — constantly shifting the incoming values from mc.sig~ up/down by an amount of up to 6 semitones.
  3. At the same time, 30 voices — the final chord, comprising 10 distinct pitches of 3 notes per pitch — are being broadcast by another mc.sig~ object.
  4. The two competing mc.sig~ values can be interpolated between by using the mix operator in a mc.gen~ object.
  5. The MIDI pitches are translated to frequencies with mc.mtof~. Keeping this as MIDI note numbers up until now is kind of nice as it allows you to think about things like detuning and pitch shifting in ‘cents’, due to the linear nature of pitch intervals in MIDI.
  6. Adjusting the main ‘Deep Note controls’ slider lets you play with the transition at step 4 in realtime. The values output by this slider object are fed into the Transition to pitch, Amplitude swell, and Pan function objects, which means that the different aspects of the sound can be independently styled while keeping the controls simple. The slider fades the sound out at either end, but bringing it in on the left side introduces the dissonant swirling noise, and dragging to the right starts the transition to ‘consonance’.
  7. The pitches produced during the transition are drawn on a stave with the nslider object, and an mc.scope~ shows the inter-pitch deviation.
  8. The sound is mixed to stereo with an mc.stereo~ object, where the placement of the different voices are subtly distributed in the stereo space by an mc.sig~ object that outputs 30 random values between 0.25 and 0.75 (due to the deviate 0.25 0.5 message).
  9. A few objects are used to roughen up the sound a little bit and boost the frequencies in the low end.

Here’s the patch if you want to have a play around:


----------begin_max5_patcher----------
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-----------end_max5_patcher-----------

For fun, try disabling the ‘Enable/disabled detune’ (step 10) to hear the difference between strictly tuned notes, and Moorer’s subtle detuning. The detuning makes it sound more rich and organic. Also, try changing the final resolution chord to match Moorer’s score (step 11). [Interestingly, the score depicts a high 89 / F5 which seems to not be present in the theme itself.]

There’s a lot of nuance to the THX Deep Note, and the end result made with Max here is similar to the original, but there are still some subtle differences. Aspects described in the score (such as how “each note moves slowly and randomly”) sounds a little more like sinusoidal oscillations in pitch in the theme (as opposed to the way they are shifted randomly by mc.rand~ in the Max version here). Rethinking the way they move randomly might be a fun exercise using mc.cycle~. There’s also a non-linear ascent to the final chord in the original which sounds like an acceleration towards resolution. Playing around with the function objects controlling the ‘transition to pitch’, ‘amplitude swell’, and ‘pan’ might be good places to start experimenting.

Links:

Pitched Synthesis with Noise Driven Feedback Delay Lines

The other day I was listening to Autechre’s Quaristice and thinking about my first perceptions of the album.  I remember thinking “This album has a very physical-modeling feel to it”.   I had forgotten about this, and recently I was playing around with Karplus-Strong string-modelling synthesis, after reading about the methodology behind it.

The opening of Autechre’s 90101-5l-l has these gorgeous rich resonating tones, which I accidentally seemed to be able to replicate with a Karplus-Strong model.  It sounds like they are capturing an incoming audio stream and then thrusting a noise-grain into a Karplus-Strong algorithm. (There’s more going on in there, but this seems to be the basis.)

Autechre – 90101-5l-l (Quaristsice)

Example of Noise-Grain Feedback using Karplus Strong Plucked String Synthesis Methods
 

In simple terms, Karplus-Strong tones are generated by taking a burst of noise, and creating a feedback loop that repeatedly lowpass-filters the noise and scales the volume back slightly.

The combination of each of these factors plays a part in the resulting tone:

  • The brighter the burst of noise, the brighter the attack and note.
  • The loop time determines the pitch (shorter = higher, longer = lower)
  • The amount of filtering determines the length and life of the note.

Kind of like concatenative synthesis with a recursive function applied to each grain.

So, for fun I was trying to make a synth that would generate tones using this noise-based feedback model using Max.

In order to generate a specific tones, I was basing my pitches on the relationship:

F0 = FS / Z-L

That is, the fundamental frequency (F0) is determined by the sample rate (FS) divided by the length of the delay line in samples (Z-L).  Put simply, the number of times the delay line is read through per second is its frequency in Hz.

My first versions suffered from a very strange thing where the pitch accuracy was shockingly bad.  I was getting weird results where tones were getting more out of tune the higher they went.

The first problem is that I was using a [delay~] delay line with integer sample-length delays.  Who would have thought that something that was ‘sample accurate’ could be a bad thing?

I realised later that it was bad because the generated tones were inversely proportional to the sample rate and that the values were being truncated to integer lengths.  When the length of the delay was long, the pitch was moderately accurate.  However, as the sample length got shorter, the pitch went way out.

The reason why this is bad is quite interesting.  Consider that we are working at a sampling rate of 44100 Hz.

What tone will be generated if we use a delay line consisting of 5 samples?

44100 / 5 = 8820Hz

What about a delay line of 4 samples?

44100 / 4 = 11025Hz

This is a big problem.  As the frequency that we are trying to generate gets higher, the less range we have in discrete tones.

At first, this appeared to be a sample rate issue.  If we increase the sample rate we should be able to get finer tone control.  However, doubling it means that we can get only one new pitch between the two we got at 44100.

88200 / 9 = 9800Hz

This is still not that good.  My solution was to make an abstraction and try some ridiculous upsampling with [poly~].  With this, understandably came a hit to my CPU.  The solution was still not all that good, as only one single new pitch could be attained between the previously possible tones each time the sampling was doubled.

This had been puzzling me for about a week until I decided to drop [delay~] for [tapin~].  Amazingly,  [tapin~] allows fractional sample length delays, as it does subsample interpolation when given a signal as its delay time.

The following is an example of the nature of the low-pass roll-off effect.  The clip starts with a fairly moderate low-pass filter (centred around 1500Hz) that is slowly opened up until it is barely filtering the delay line.  As the filter starts out strongly attenuating, the note is quickly damped, and demonstrates a transition from:

Muted > Damped > Koto > Plucked Bass > Slap Bass > Harpsichord > Non-Realistic Model of a Resonating String.
[Examples of Simple Plucked String Synthesis with a Relatively Bright Pink Noise Excitation.]

A simple version of the patch can be downloaded here: Karplus-Strong example