Tuesday 7 April 2020

Sound Design: Ping-Pong sound in Ableton Live

In a complete break from the traditional content on this blog, here's a quick bit of sound design.

How to make a sound that works well to accompany a ping-pong video where a bat hits a ball... 

Piano roll a G3 and then a G4, a bar apart. For some reason, octave intervals work well for this type of sound... Try changing the intervals and see! I think it is something to do with the two different pitches being perceived as being at different distances or positions, but I've never managed to find any published research on this topic. (Which doesn't mean there isn't any, of course - one of the fascinating things about the InterWeb is that you can't always find things... Searches are not perfect, or deterministic...)


Take a sine wave, give it a fast attack, 80 ms decay, sustain zero, no release, and use a pitch envelope to pull it up from about 6 semitones down at the start of the note, pretty quickly.

The sine wave is used purely because many real world objects have a tendency to oscillate with the simplest possible waveform (and arguably the most efficient: the sine wave uses the least energy to wobble!)

The fast attack is because the transfer of energy from a hard (-ish) bat to a (hard) ball happens quickly. Compare and contrast the sound made by the strings on a tennis racket when it hits a fluffy tennis ball.

The slightly slower decay is just long enough that you can hear it (80ms is about ten times the shortest sound that you seem to be able to perceive, which is why a 'fast' 5ms attack time seems like it is fast!) and not long enough so that you become too distracted by the pitch.

The rising pitch envelope at the start of the sound adds to the natural-ness of the sound. Real-world sounds often seem to take time to get into a stable oscillation, and so this is a way of sign-posting that this is a sound that is meant to be used in a naturalisic context.

(Of course, for a true 'real' sound, then a recording of the actual sound would appear to be the best one to use... But this assumes that the actual sound is what people expect and is effective! I'm reminded of the sound of a soft drinks can being opened and the frothy liquid being poured into a glass that was synthesized by Suzanne Ciani many years ago...)

Which produces:

You might have noticed that the Noise generator is turned on, but with a very low cut-off on the 'Color' low-pass colour filter. This is very 'red' noise, and is used to add a bit of extra 'bat hits ba;;' randomness to the start of the sound. A more sophisticated implementation would use two synthesizer sound sources: one for the sine wave, and another for the noise burst (probably with a faster decay). For this simple example, I have just added in a bit of noise to the sine wave.

This 'tone plus noise' technique is usually credited to the French composer Jean-Claude Risset, and some drum synthesizer methods are often referred to as 'Risset' drums (For example: there's a 'Risset Drum' plug-in included in the Audacity audio editor software.). This works very well - using band-pass or resonant low-pass filters to filter noise so that it adds uncertainty to a low frequency tone is very good for emulating many drum sounds, and is used on some classic 70s (and 80s, even though samples were becoming increasingly popular) drum machines.

So that's the 'generation' part of the sound done. Note that the filter is wide open - using a resonant low-pass filter on a sine wave is usually spectacularly unimpressive. Now to the 'processing' part.


Next, apply a bit of hard saturation with soft clipping, followed by compression to tighten it up. Finally, wet reverb in high quality mode with early reflections, reflect and diffuse full on, and sized to taste.

The saturation-based waveshape 'distortion' is to add a bit of non-linearity to the louder parts of the sound. A pure sine wave sounds boring, and so adding a bit of 'over-drive' makes it sounds more 'real'. Imperfections are often what turns a synthetic sound into one that is more interesting and less 'synthetic'. The compression enhances the decay, and it also sounds like a compressor - which is another interesting imperfection: your ear knows what a compressor sounds like, and so putting a compressor in the sound tells your ear that you are hearing a sound that has been recorded. Adding in an artificial noise floor might be another method of adding fake cues for 'reality'.

(The real experts in using subtle cues to make audio sound real are the people who add sounds to movies and TV. For animations in particular, there are no sounds with the pictures, and so everything needs to be added: rustles, bangs, knocks, footsteps, soft drinks cans being opened, kissing, cutting bread, slurping coffee and more. This process if called 'Foley', named after Jack Foley, who was one of the people who used a wide variety of props to add sounds to moving pictures. Of course, a Foley artist would probably use a bat and ball for this particular piece of sound design...)

The reverb is really two things: the early reflections and the 'space'. The rapid echoes known as reflections accentuate the sharpness of the attack, and they emphasise that energy has been transferred. Blockbuster movies use a variety of busy, wobbly or low, growly sounds to indicate the movement of power, and these are so ingrained in what people expect that it feels wrong when you don't get them in real life. Spaceships in space don't make sounds, and yet you 'know' (and expect) that all of that pent-up energy required to thrust them into hyper-space just has to make a sound! Without the sound, it would feel 'fake'...). The 'space' part of the reverb is to give the listener a sense that the focus of their attention should be the bat hitting the ball - everything else goes 'out of focus', but it also imposes an artificial spacial environment that isn't present in reality. The apparent big reverberant space gives the sound gravitas, importance, significance - it screams (gently): 'Watch me!'

Which all looks like this in Ableton Live stock audio effects:


The resulting sounds are available on SoundCloud. The demo track contains just two notes: a G3 and a G4. (using the Ableton 'C3=60' note naming convention) The result is not perfect (and what is?), but imho a good starting point for this type of sound... You should use this tutorial as a starting point to exploring with your own personal variations - just copying what I've done will only get you part of the way along the lifetime quest that is sound design. For further study, you could compare and contrast my sound to commercial examples in music tracks and sound libraries...


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