Quantization can refer to a number of different processes depending on the context, and we already discussed one meaning when we looked at analog-to-digital signal conversion. However, nine times out of ten when someone mentions quantization in the context of music production, they're referring to it as a tool that aligns notes or drum hits to the nearest beat. Quantization generally refers to MIDI data, and a MIDI piano roll is probably the easiest way to visualize the process.
How Does It Work?
The quantization process works by moving each MIDI note so that it starts precisely on the nearest beat. But what do we mean by 'the nearest beat'? In order to quantize MIDI note data it's necessary to decide what resolution the notes will be quantized to. This determines how many sub-divisions will be defined per bar. These sub-divisions are the beats that our notes will be aligned to. In the basic quantization process, the resolution is the key factor in determining which beats the notes are moved to. If we quantize to 1/8 note resolution, each note is moved to the nearest 1/8 note - if we quantize to 1/16 note resolution, each note will be moved to the nearest 1/16 note, and so on. Choosing too low a resolution will result in notes being moved drastically from their original positions and lose the detail of the sequence.
Too high a resolution will result in notes slipping through the net or not being moved far enough to come into line. Although it's most often used for MIDI, quantization of note data also takes place in other types of sequencer. For instance, older drum machines with internal sequencers use a basic form of quantization during recording to align notes to a grid.
Although you often don't know it's going on, any drum machine which tidies up your timing inaccuracies and shifts the drum hits onto the beat is quantizing for you. Note that quantization only really applies to recorded sequences rather than live performance, for obvious reasons. Real-time quantization of live performances is practically impossible since notes can only be delayed to the next step on the grid (moving them forwards in time would require them to play before you hit the key!).
Swing and Feel
The main problem with quantization is that 1t completely removes the human element from the timing of your notes. As a result, a quantized part often sounds robotic, with a relentless straight beat. Tiny timing inaccuracies are a very important part of the feel of your music, and quantization unfortunately makes it all too easy to suck the life out of a part at the click of a button.
There may be occasions when perfectly straight rhythms are desirable, but the rest of the time we need to come up with some kind of solution for improving timing while also maintaining feel and groove. The most basic method is to apply quantization using swung rhythms. Swing settings use a particular form of quantization which still moves notes to pre-defined positions, but crucially in this case the pre-defined bar sub-divisions aren't perfectly evenly-spaced as they would be with straight 1/8 or 1/16 note quantization.
You should be able to see in the piano roll how each even-numbered l /8 note has been pushed back ever so slightly, with the resulting lazy sound giving a more interesting human feel to the beat. Swing quantization also comes in very handy for adding groove after entering notes directly into the piano roll. In practical terms, there's also an even easier option for maintaining feel when applying quantization, and it's simply a case of not processing so many of your parts.
It can be tempting when writing and producing to listen to each part individually and tighten everything up, but the human element comes from the slight inaccuracies and deviations from straight timing. One effective method is just to quantize some of the notes, usually the ones which hit the 1/4 note or 1/8 note beats. This is particularly effective with drums.
Quantizing the beats on the first and third quarter notes of a bar, or just quantizing the kick drums, creates a rigid backbone that the other beats can groove around. This can either be done manually or using automatic features such as Ableton's Partial Quantize.
To add even more human feel and groove to quantized sequences, most MIDI software also now allows you to apply customizable groove templates to patterns. The concept rs exactly the same as regular quantization, with notes being moved to the nearest of a pre-defined set of positions, but these positions are entirely at the user's discretion. Perhaps most interestingly, it's also possible to analyze the transients of an audio loop in order to determine the positions of its beats and convert this into a custom groove template that can be applied to MIDI sequences. As such, quantization templates can be used to apply the groove characteristics of one loop onto another, or to ensure that the groove of a MIDI part sits nicely with audio loops. It's an extremely powerful approach that has all kinds of uses regard less of what style of music you're making.
So far we've mainly been talking about quantizing MIDI sequences, but developments in audio processing over the last decade mean that it's now well within the reach of most home producers to quantize audio as well as MIDI data. lime stretching technology allows notes which are out of time to be pushed and pulled around until they hit the precise beat you want them to land on.
Effects such as Pro Tools' Beat Detective and Logic's Flex Time allow you to apply a quantization effect to an audio recording just as you would for MIDI data, with the complex audio processing being handled for you behind the scenes. The software detects the transients of your recording and automatically slides sections of the audio around to push them onto the beats. In theory it's pretty simple, but the reality rs that audio quantization isn't easy to get right with presets and a bit of manual tweaking is likely to be necessary for the best results It's also possible to use the same theory behind MIDI groove templates to adjust the swing and groove of your audio tracks. Want to steal the groove of a particularly funky drum loop and apply rt to your bassline? No problem. Analyze the audio drum loop, detect the transients, convert it to a groove template and then apply it to your original bass audio. Ableton Live probably offers you the most advanced options when it comes to handling complex audio groove adjustment, but similar effects are now possible in most DAWs.
Finally, there's one more form of quantization which is worth considering here. So far we've looked exclusively at timing-based quantization methods, which shift sounds to the nearest pre-defined value on a time scale, but it's also possible to quantize sounds by pitch, moving them up or down the frequency range to the nearest pre-defined value. In MIDI terms, this is a relatively easy process. Each note which doesn't fit into your selected scale simply needs to be transposed up or down to the nearest note which fits.
Many DAWs now include MIDI pitch quantization effects in the form of preset scales. In Ableton Live, for example, pitch quantization is easily achieved by dragging the Scale effect to a MIDI track and then selecting which notes you want to quantize the MIDI signal to. DAWs wrthout a MIDI pitch quantization feature can still achieve the same effect using MIDI note mapping or a plug-in such as Mucoder Tonespace. Audio pitch quantization is a little more involved but can be achieved using pitch correction tools such as Antares Auto-Tune. The correction process transposes sung notes to the nearest note on a pre-defined scale in order to achieve higher levels of pitch accuracy.
With all these tools at your disposal there are no longer any excuses for sloppy timing or inaccurate pitch!
What is Swing?
In musical theory, swing refers to a playing style in which notes of theoretically equal length are played with variation, alternating between one slightly longer note and one slightly shorter in order to create a grooving syncopated rhythm. In Electronic music, swing is also sometimes referred to as shuffle (although this is technically incorrect in terms of musical theory). It's a very simple technique that is incredibly useful for adding groove and movement to a track, and it's been a mainstay of Electronic music since its inclusion on classic 1980s drum machines.
In the context of quantization, swing may be applied by shifting the starts of notes around rather than extending them. With percussive sounds especially, it's not a problem if the sounds overlap so we're less interested in the length of notes than their start points. Swing is also sometimes expressed as a percentage, with the figure referring to the length of the first note relative to the whole of the two notes.