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More Fun in the Waves (Part 2) | |
Article from Music Technology, October 1988 |
Following last month's explanation of computer-generated waveforms and their uses, we look at strings of waveforms working together to build complex sounds. Tom McLaughlin investigates wavetables.
Want to increase the scope of your sampled sounds or additive waveforms? Linking waveforms together will enable you to produce sounds that can be realistic or unnatural.
SEAMLESS LOOPS CAN actually be designed into a progression. Yeah, you can loop around a cycle or two of many sounds and get away with it, but it will lack animation. Even the smallest amount of harmonic movement adds life to loops. Something as simple as slightly modulating the fundamental or second harmonic's amplitude makes a significant difference.
Loops can be made from sound material approximating the steady-state tone colour of a sample and crossfaded through those sounds where loops are difficult, impossible, or where loop material is nonexistent. It's a technique not unlike Roland's L/A synthesis really.
Be tasteful with the severity of harmonic movement within a loop unless you like more severe effects - gently swept harmonic cycles sound more natural to the ears. If you're working with sampled source material, try isolating segments that flow smoothly from one to another. With additive synthesis you'll want to change the levels of harmonics only a little from one to the next for a natural movement. Crossfading between members of a wavetable will give you smoother transitions, but if care is taken in the first place you may not need to resort to crossfading at all.
That said, there should be nothing to stop you constructing loops with wide variances in tone colour between segments, it's just that you're not used to hearing sounds like this. You may stumble upon some very useful sounds - especially when played back so fast that you can't hear the changes.
Making loops can be approached in two different ways. Segments that flow from one to another then back to the beginning of the loop again give a natural sound, but it can be time consuming to refine these ideal segments. A more practical method is to derive several segments that flow from one to another then reverse their order - A-B-A; A-B-C-B-A; A-B-C-D-C-B-A.
The series returning to segment A may sound strange. You'll need to reverse and invert the phase of each segment to get the most from this loop construction technique.
Loops within loops often help conceal the tell-tale loop cycles. A loop 32 segments long can have sub-loops occurring every 16, 8, 4 and 2 segments; a loop 24 segments long every 12, 8, 6, 4, 3 and 2 segments. With additive synthesis, try a slight modulation in amplitude with different harmonics having differing "sub loop" cycles.
I LIKE STEREO effects - stereo echoes, chorus effects and different reverbs on each side of a stereo mix. Before the introduction of that second audio channel we could either make things sound close up or far away: crisp 'n' clear or smothered in reverb. That was about it. With wavetable synthesis we can design stereo effects into wavetable progressions - amplitude panning, timbre panning, tuning and phase panning. A stereo effect that's easy to program into two wave-tables is a simple panning loop. (See Figure 2)
A stereo Leslie effect can be created by making the front, left and right waveforms brighter than the rear. The effect you're trying to create (best assessed when wearing a pair of headphones) is for the sound to move around your head in a circle. If you're using crossfading between segments and have the facility, experiment with different fade curves (linear, exponential and so on) for different movement effects. (See Figure 3)
SOMETHING I MISS from analogue synthesis days is playing around with pulse-width modulation. Although easily executed in a variety of manners on inexpensive analogue synths, anything resembling PWM has to be first designed and calculated, then programmed with additive synthesis - it's often a lot less work to sample an analogue synth. Far more suited to computer programming are modulations to/from/between different tone colours, phase and pitch relations. If you're going to make the effort to construct a wavetable tone progression you might as well go for something new and unusual. You just might invent the next flavour of the year. Why not try designing one wave colour to invert its phase while transforming into another colour, have all the even harmonics start sharp and the odd ones flat, modulate the pitch of specific harmonics or rapidly modulate the amplitude or phase between adjacent harmonics or harmonic clusters?
MANY THINGS WE take for granted on synthesisers and samplers turn out to be laborious or frighteningly complex programming jobs with additive synthesis. But flanging effects are no more difficult than layering the same sound on top of itself. Play them back at the same exact time and pitch and you probably won't hear anything, but playing one back slightly later or out of tune (static or modulated) with the other will produce phasing/flanging. And the effect can be very deep and wide. A new palette of flanging effects lie waiting to be discovered with a technique available on any sampler capable of playing two samples at once. Bright samples with a fair amount of harmonic movement will give the most dramatic effects. Loops give a constantly changing phase "swirl" with one slightly detuned, the severity of phase cancellations increasing the more in tune they are.
THE POWERFUL COMPUTING software of some samplers allows natural sounds to not only be digitally recorded and played back, but also analysed and resynthesised according to Fourier's theory. This is one of the most important things about sampling as it pertains to acoustic research and creative synthesis. Never before has musiciankind had the means to examine and recreate sound in such minute detail. Although on the expensive side at the moment, the computer musical instruments and software packages capable of carrying out these calculations are becoming more affordable year by year. The catch still seems to be (for most of us anyway) that unless you spend time with tuning or vari-speeding recordings of instruments when sampling, or own a system that has a comprehensive sample rate conversion program, there's very little chance that when you mix any wavetable, sampled or re-sampled sounds, they'll end up anywhere near in tune with one another to be musically useful.
You can layer different sounds after tuning them and play them back at the same time. With truly interactive sample resynthesis and wavetable software, something very much like Eventide's pitch "harmonizing" can be achieved by keeping the timing of a sample/wave progression constant while the pitch changes, by dividing the sound material up into segments, discarding or adding space between them and carrying out a crossfade from one segment to the next. The reason I bring this up is that the new age of computer musicians will not realise the full potential of our new-found sonic freedom until we can muck around with both sampled (acoustic and synthesised) and digitally created (synthesised and resynthesised) sounds.
I'LL LEAVE YOU with an esoteric approach to creating sounds from additive synthesis tables. For those of you into the nitty gritty side of things by designing additive sound waves from the bottom up, an approach to stringing together wavetables is to think in terms of chords or chord progressions. There are many chords to be found hidden within the harmonic series. Harmonic effects rarely, if ever, occurring in real life can be fashioned using wavetables. Intervals foreign to our Western music system are present that may be used to create tension within a progression. For something much more bizarre than even the most over-the-top analogue filter sweep effects, try programming a "circle of fourths or fifths" wavetable, ending up on the fundamental chord.
Progressions may be thought of in terms of block chords or counterpoint. You can experiment with the chord progression of a song's hook line or chorus to reinforce it in the mind of the listener in a subliminal fashion. There's no reason why melodies couldn't be programmed into a wavetable, even entire arrangements in four-part harmony are possible for those with enough patience.
This is the last part in this series. The first article in this series is:
Fun in the Waves
(MT Sep 88)
All parts in this series:
Part 1 | Part 2 (Viewing)
Dumping Grounds (Part 1) |
The Ins and Outs of Digital Design |
The Poor Man's Guide to Clap Sounds |
A Handy Way To Solve Sticky Control Problems |
Total recall - Cosmology |
Understanding the DX7 (Part 1) |
Hands On: Yamaha DX7 |
Photographing Sound - The Art of Sampling (Part 1) |
Customise (Part 1) |
Patchwork |
Hands On: Korg M1 |
Sweetening the pill - Sampler test |
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Feature by Tom McLaughlin
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