1 / 17

EE2F2 - Music Technology

10. Sampling. EE2F2 - Music Technology. Early Sampling. It’s not a real orchestra, it’s a Mellotron It works by playing tape recordings of a real orchestra Each key starts the relevant tape playing When the key is released, the tape rewinds automatically

bevan
Download Presentation

EE2F2 - Music Technology

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. 10. Sampling EE2F2 - Music Technology

  2. Early Sampling • It’s not a real orchestra, it’s a Mellotron • It works by playing tape recordings of a real orchestra • Each key starts the relevant tape playing • When the key is released, the tape rewinds automatically • The tapes are only 8 seconds long though, so notes can’t be held any longer Listen to the backing violins in this David Bowie recording from 1969.

  3. Digital Sampling • With modern computers, it is fairly trivial to digitally record sounds into memory (or disk) and then play them back in response to MIDI commands • To create a digital version of a Mellotron you need to record the instrument(s) separately for every possible pitch. • Extra desirable improvements: • Extending the playback time • Managing the memory/recording requirements • Introducing velocity sensitivity • Modifying the recordings to produce new sounds

  4. Memory Requirements • Early digital samplers were heavily restricted in memory • For example • Ensoniq Mirage (1985) • 8 bit resolution • 144 kbytes memory, 32 kHz sample rate • 4.6 seconds recording time • Mellotron (1963) • 35 notes each with 8 seconds of tape • Total = 35 x 8 = 280 seconds recording time • How could just 4.6 seconds be any use?

  5. Looping • After an initial attack portion, many sounds don’t actually change that much with time • Instead of sampling several seconds of a sustained note, it would save memory to just repeat (or ‘loop’) a small section • Unlike tape, digital memory can be accessed randomly, so looping is fairly easy Flute sample With looping

  6. Example! Advanced Looping • Looping points must be chosen with care to avoid: • Big changes in the volume of the sound (creating a ‘pumping’ effect) • Changes in phase (creating audible clicks) E.g. 1 E.g. 2

  7. Example! Pitch vs. Playback Rate • Compare these two flute samples • The waveform shapes are virtually identical • The higher note can be generated by playing the lower note at a faster speed • Being a semitone apart, the ratio between the speeds is 1:21/12 = 1:1.0595 Flute (F4) Time Flute (E4) Time

  8. Example! Multi-Sampling • If you speed up a sample: • The pitch rises • The entire frequency response of the instrument is effectively shifted • Result: it starts to sound ‘squeaky’ • If you slow down a sample: • The pitch falls • The frequency response changes too • Often, the resulting sound lacks upper harmonics • It sounds thin, hollow and simply wrong! • Solution: Multi-sampling

  9. Velocity Variations • Up to now, our sampler doesn’t respond to velocity • Acoustic instruments respond in terms of: • Amplitude: Higher velocity = Louder • Envelope: The sound can evolve in a different way • Timbre: Spectrum changes with velocity • Amplitude and frequency variation could be achieved using an amplifier and a filter (more later) • Alternatively, record samples of the actual sound for different velocities

  10. Example! Cross-Fading • In a multi-sampled set-up, the sample used for any note can depend on: • Pitch • Velocity • The simplest implementation is to allocate each sample a ‘zone’ in pitch/velocity space • This can mean there is a sudden transition when crossing zone boundaries • To prevent this, interpolation (or cross-fading) can be used

  11. Sampling Limitations • Sampled instruments can sound very realistic but they do have some notable limitations: • High memory demands • It’s difficult to sample expressive instruments whose sounds can evolve in response to the performer • Only real instruments can be sampled! • A way of addressing some of these issues is to combine sampling and subtractive synthesis techniques • Such instruments are known as sample & synthesis instruments

  12. Amplitude and Timbral Control • As noted before, acoustic instruments respond in terms of: • Amplitude: Higher velocity = Louder • Envelope: The sound can evolve in a different way • Timbre: Spectrum changes with velocity • All these effects can be modelled using familiar processes • Amplitude changes can be synthesised using an amplifier • Envelope changes can be synthesised by varying the parameters of an envelope generator • Timbral changes can be synthesised using a filter • All of these are found in a subtractive synthesiser

  13. Sample + Synthesis • This diagram is identical to the subtractive synthesiser except that the V.C.O is now a sampler • It can be playing very short loops or entire recordings Multi-sample playback V.C.F. V.C.A. Output L.F.O. Trigger Env. Gen.

  14. Example! Using Sample + Synthesis • Some examples of how sample+synthesis can be used: • Instead of recording multiple velocity samples, just record one loud sound and model velocity effects using a filter and amplifier • To apply performance effects like vibrato or crescendos, use the LFO or amplifier respectively • To create entirely new sounds, use the processes in the same way as an analogue subtractive synthesiser

  15. Comparison with Analogue Synthesis • Amongst the samples stored in memory, standard waveforms like sines, squares etc. can also be stored • The sample & synthesis structure can, therefore, do everything that a subtractive synthesiser can • Only notable exceptions in early models are large frequency sweeps (portamento or ‘slide’), especially when using multi-samples • The latest instruments can even handle this.

  16. Pros & Cons • Pros • Very convincing, realistic sounds are possible • Compared with other techniques, it’s relatively easy to program a sampler • Cons • Hard to innovate and produce novel sounds – only real instruments can be sampled • Very unconvincing performances are possible – some instruments don’t sample well Suitable Unsuitable Pianos Drums Ensembles Solo strings Solo brass Individual voices ‘One-shot’ sounds or relatively inexpressive Expressive sounds. Smooth transitions between notes.

  17. Summary • Sampling • Playback of pre-recorded sounds • Pitch can be varied by changing playback rate • Multi-sampling improves quality over whole pitch & velocity range • Sample + Synthesis • All the benefits of high quality sampled sounds plus the ability to form novel instruments • Easily the most popular technique currently used

More Related