What is a MIDI Sequencer?

History of electronic music synthesis

    Electronic music is a relatively new phenomenon. Spawning from post-world war two England, electronic synthesis was pioneered by composers turned engineers like Tristram Cary and David Cockerell. In the early days of electronic music synthesis, analog signals were routed or "patched" in and out of various "modules" that contained a variety of Oscillators, Filters, effects and controllers.
 
    A basic synthesizer contains a voltage controlled oscillator that will oscillate at a given frequency depending on a voltage routed to its input, and a controller of some sort (a keyboard perhaps) that outputs a given voltage for a given note. To create complex melodies however, a way to automate music is required. Creating arpeggios for instance is a relatively simple concept musically, but doing so from an automated standpoint has been solved through the use of a device called a sequencer. A sequencer is nothing more than a device that will in the end, create a string or sequence of notes, then repeat that same sequence over and over again.

Analog vs digital note representation  

    Once analog synthesizers were developed to a point of accurately mirroring the musical scale, they utilized a fairly standard way of representing a musical notes, called 1 volt per octave scaling. The 1 volt/octave system was a way of having a VCO (voltage controlled oscillator) output a precise musical tone in increments of 0.0833 volts. This system however provides no quantization of frequency, this is to say that any frequency between musical notes may still be expressed. In this respect, analog synthesizers may be more versatile than  newer synthesizers, but are still harder to control in a way that yields to conventional music theory when using a non-key based control device.

    With the advent of digital computers, a new standard system for representing musical notes was developed, this system is known as MIDI. MIDI is a serial data transmission protocol that is used to represent musical information in the form of note, velocity (volume) and aftertouch. Notes are represented by a 7-bit binary number, with decimal values ranging from 0 to 127, giving MIDI the ability to express a total of 128 musical notes. MIDI can also be used to transmit other bytes of data known as status and data bytes.

*The various intricacies of the MIDI protocol are elaborated on further in the blog.

Advantages and disadvantages

Representing musical notes as electronic signals is a very useful notion, but the various methods to do this each have their own pros and cons, MIDI for example requires first for a musical device to be MIDI compatible, MIDI also requires multiple bytes of information to represent audio frequencies between that of musical half tones, that is to say a frequency between a C4 and a C#4 for instance.