A sampler is an electronic or digital musical instrument which uses sound recordings (or "samples") of real instrument sounds (e.g., a piano, violin or trumpet), excerpts from recorded songs (e.g., a five-second bass guitar riff from a funk song) or found sounds (e.g., sirens and ocean waves). The samples are loaded or recorded by the user or by a manufacturer. These sounds are then played back by means of the sampler program itself, a MIDI keyboard, sequencer or another triggering device (e.g., electronic drums) to perform or compose music. Because these samples are usually stored in digital memory, the information can be quickly accessed. A single sample may often be pitch-shifted to different pitches to produce musical scales and chords.
Often samplers offer filters, effects units, modulation via low frequency oscillation and other synthesizer-like processes that allow the original sound to be modified in many different ways. Most samplers have Multitimbrality capabilities – they can play back different sounds simultaneously. Many are also polyphonic – they are able to play more than one note at the same time.
Usually a sampler is controlled by an attached music keyboard or other external MIDI controller or source. Each note-message received by the sampler accesses a particular sample. Often multiple samples are arranged across the keyboard, each assigned to a note or group of notes. Keyboard tracking allows samples to be shifted in pitch by an appropriate amount, typically in semitones and tones. Each group of notes to which a single sample has been assigned is often called a "keyzone", and the resultant set of zones is called a keymap.
For example, in Fig 1, a keymap has been created with four different samples. Each sample, if pitched, should be associated with a particular center pitch. The first sample (Violin G#2) is distributed across three different notes, G2, G#2, and A2. If the note G#2 is received the sampler will play back the Violin G#2 sample at its original pitch. If the note received is G2 the sampler will shift the sample down a semitone while the note A2 will play it back a semitone tone higher. If the next note (Bb2) is input the sampler will select the Violin B2 sample, playing it a semitone lower than its center pitch of B2.
In general, samplers can play back any kind of recorded audio. Most samplers offer editing tools that allow the user to modify and process the audio and apply a wide range of effects. This makes the sampler a powerful and versatile musical tool.
Many samplers work as described above: the keymapping system "spread out" a sample over a certain range of keys. This has side-effects that may be desirable in some contexts, such as speeding up or slowing down drum loops. However, the higher and lower-pitched parts of such a keymap may sound unnatural. For example, if a harpsichord is sampled in its lower register and then the samples are moved up to very high pitches, the high notes may not sound natural and authentic. When arranging a pitched instrument over several keymaps, the transition from one to another may be too noticeable for realistic imitation of the instrument – the art is to make transitions as smooth as possible.
Some phrase samplers are more optimised for triggering single "one-shot" sounds such as drum hits. Each keymap spans only a single key, requiring a large number of zones (61 on a five-octave keyboard), each with its own settings. "Phrase sampling" aims to simplify this, particularly on interfaces such as the 16 pads on the Akai MPC series: the fact that each pad is actually a note is hidden from the user. The sampling engine does not re-pitch samples, it only plays them back. The user interface is simplified. Phrase samplers often have a groovebox format, which makes them lightweight, easy to operate and light to carry.
Samplers can be classified by several specifications;
- Polyphony: How many voices (or notes) can play simultaneously, to create chords
- Sample Space: How much memory is available to load samples
- Channels: How many different MIDI channels are available for different instruments
- Bit depth: How much sample resolution can be supported
- Outputs: How many discrete audio outputs are available