Midi Effects

MIDI is a standard to handle performance data, not performance per se. Midi data allow us to know which notes were played, how long and how hard or soft and what musical instrument (electronic) done it. If these data are saved, they can be played later making them seem as a performance were really saved. However we have to remember this isn't so. They are only data and they can be handled freely.

On the other hand, is very common to use audio effects to alterate amplitude, timbre, frequency and duration of audio signals and is a thoroughly extended practice, but... Is it possible to simulate the same effects using just MIDI? Is there a way to obtain the same (or equivalent) results to audio effects when a performance is played?

The answer is yes, though the complexity degree varies. Midi effects can be devided in two big categories:

• MIDI effect to alterate file structure.
• MIDI effects to simulate audio effect.

As an historic datum, the first sequencer to use midi effects to alterate the natural flow of performance (without destroying it) was Bars & Pipes, a Commodore Amiga program which for long time was imitated but never matched. Subsequently, Microsoft bought the technology to implement his Direct X Sound API. Meanwhile Steinberg took the idea and improved it to come up with the VST (Virtual Studio Technology) standard.

Structure MIDI Effects

These kind of effects are mainly data filters which handle some parameter from the MIDI protocol. For example, it's possible to filter out (remove) an instrument without loss of quality in the performance (of course, quality not meaning the missing instrument). It's posible to change volume (gain), vibrato and modulation of just one instrument or a range within an instrument leaving untouched the rest of the composition. It's possible also, change the performing instrument for some part of the piece or to combine two or three instruments into one or the other way around: make several instruments play some parts of what was played for just one original instrument. Also, composition transposing can be achieved without phase shifting issues.

Some of these effect are achieved through file edition inside the MIDI sequencer program because they are one-time changes, but there are others which carry dedicated processes and make the same processing for any data flowing thru them.

Audio MIDI Effects

These type of effects try to simulate equivalent audio effects through data manipulation in order to resemble delay lines, chorus, reverbs, filter resonance, equalization, compression, etc.

For these effects to get this purpose, they have to manipulate heavily the original file data, adding or removing midi events before the time of final reproduction to attain the intended effect. If this manipulation is too much and the needed time to make the processing is greater than the required time to achieve the effect, the effect won't be reproduced convincingly.

However, real CPU operation speeds allow us to reproduce mostly any known effect without big problems.