FM Synthesis
Until recently, major sound card manufacturers used FM synthesis to support MIDI playback. FM synthesis mimics musical instruments, drums and special effects by mathematically manipulating simple sine waves. FM synthesis techniques use one periodic signal (the modulator) to modulate the frequency of another signal. If the modulating signal is in the audible range, then the result will be a significant change in the timbre of the signal.

Wave Sample Synthesis
Rather than manipulate sine waves, Wave Sample synthesis uses high-quality, digitally recorded samples as a basis for creating sounds. The result is an overall sound which is much richer and more realistic than that of an FM synthesized sound.

Synthesizing musical instruments from sampled sounds is considered an elusive art. It is the art of knowing which samples to store, how to store them, and most importantly, how to electronically manipulate or modulate them to reproduce sounds that closely approximate the sounds of the "real thing". This modulation of sampled sounds is the essence of wave sample synthesis.

Wave sample synthesis systems use a variety of special techniques to get more types of sounds from a given amount of memory.

For example, in order to minimize sample memory requirements, wave sample synthesis uses pitch shifting, or pitch transposition techniques, to generate a number of different notes from a single sound sample of a given instrument. For example, if the sample memory contains a sample of the middle C note on the acoustic piano, then this same sample data could be used to generate the C# note or D note above middle C using pitch shifting.

Vibrato and Tremolo are effects which are often produced by musicians playing acoustic instruments. Vibrato is basically the low-frequency modulation of the pitch of a note, while tremolo is the modulation of the amplitude of sound. These effects are simulated in synthesizers by implementing low-frequency oscillators (LFOs) which are used for modulating the pitch or amplitude of the synthesized sound being produced.

Understanding MIDI
MIDI (Musical Instrument Digital Interface) is an international hardware and software standard. It specifies the hardware interface that allows you to connect electronic musical instruments and computers produced by different manufacturers. It also specifies a communication protocol for passing information from one device to another. MIDI devices communicate with each other through this MIDI interface.

Understanding MIDI Files
A MIDI file is a standard file format for storing recorded MIDI information. It contains notes, timing, and instrument designations for up to 16 channels (musical tracks). The file also contains information about each note, including the key, channel number, duration, volume and velocity (how quickly the key travels to its down position when struck).

Understanding MIDI Channels
A MIDI channel is a passage through which musical information can flows from one main device to another. MIDI channels are similar to musical tracks. MIDI files combine 16 channels of information to form a song. The MIDI patch assignments refer to MIDI channel numbers 1 through 16. With this structure, it is possible to record piano, flute, trombone and timpani and then play them back all at once.

Understanding General MIDI
To ensure that MIDI files created on one MIDI device can be accurately replayed on another manufacturer's MIDI devices, a standard patch known as the General MIDI standard is adopted.

The General MIDI (GM) system specification has gained wide acceptance from the most common PC/MIDI manufacturers supporting MIDI in Microsoft Windows.

By conforming to this standard, software developers can now send GM commands to any GM hardware device and be assured that the hardware will 'understand' what it is receiving. In turn, hardware manufacturers who produce GM devices know the exact features that their device must support and the commands that need to be processed. Thus, the GM devices will enjoy compatibility with a large number of software application. For users, music and sound effects in multimedia and entertainment titles can be played back in a way that closely follows the composer's intent independent of the hardware being used.

General MIDI Standards
General MIDI devices must support a pre-defined set of musical instruments, sound effects, and drum kits. Each of the 128 sounds in GM are assigned to a specific patch number to ensure that proper instruments are used during recording and playback. Also, a minimum of 16 MIDI channels must be supported with at least 24-note polyphony and a specified set of controllers.

Note: Channel 1 to 16 are reserved for synthesizer data and channel 10 is reserved for key-based percussion instruments.