Creating Digital Audio (2)

Digital Synthesis of digital audio

This method is used to generate unique sounds directly without any analog to digital conversion. Obviously you can not create human or realistic sounds with this approach.

The method involves generating the appropriate samples directly which would have been otherwise produced when an ADC sampled an analog signal with a specified sample rate.

As long as we know the waveform and frequency of a certain kind of sound, we can re-create it through software using this method. However the sound produced may not sound very realistic. Modern day music software use this technique to produce some unnatural sounds.

For example we can write a program to create a sine wave signal’s sampled values using some arithmetic in our program. The sequence of these samples can be replayed to create the sound of a sine wave.

Synthesizers –Devices which are capable of generating (synthesizing) sounds are called synthesizer. They can be played by a human just like any other instrument such as flute or guitar. The theory behind them is to imitate the mechanism of sound production electronically.

A synthesizer is a very versatile musical intrument. First of all it can produce a variety of sounds such as piano, violin, flute, bass , strings and many more. You can play all these musical instruments using a single synthesizer. You press few buttons and program it to play like flute or piano or whatever you like.
There are both analog and digital synthesizers available in the market. Analog synthesizers were the first to hit the market in 70s.

Analog synthesizers mimic the mechanism of natural sound production involving vibration, modulation and pitch just like humans produce sound by vibration of our vocal chords Analog synthesizers use amplifiers, filters ,oscillators, enevelop generators to produce sounds various kind of sounds.The sound is produced by various settings of these modules under human control.
Moog, Corg, Yamaha, Roland manufactured these analog synthesizers.

Picture on left shows an analog synthesizer.

A digital synthesizer is a synthesizer that uses Digital signal processing (DSP) techniques to make musical sounds. They directly create digital samples of sounds by mathematical computation of binary data. They can transform the samples in more than one ways to give special effects to the sound or give a different pitch to the sound.

Early commercial digital synthesizers used simple hard-wired digital circuitry to implement techniques such as additive synthesis and FM Synthesis. Other techniques, such as Wavetable Synthesis became possible with the advent of high-speed microprocessor and digital signal processing technology. We will talk about synthesis techniques little later in this chapter.

Digital synthesizers are realized in a separate hardware which very much looks like a music instruments. Synthesizers typically have a keyboard which provides the human interface to the instrument and are often thought of as keyboard instruments. However, a synthesizer's human interface does not necessarily have to be a keyboard, nor does a synthesizer strictly need to be playable by a human.

A software synthesizer, also known as a softsynth or virtual instrument is a computer program for creating digital audio. It works like a common synthesizer, but is realized entirely in software.

A software synthesizer can use many methods of generating sounds. They can implement oscillators, filters and enevelop generators in the software itself which is similar to analog synthesizers or can use wavetable synthesis techniques (which uses sampled sounds described later) to produce the sound of various muscial instruments.

Another way software synthesizer can produce sounds of any musical instrument is by allowing the user to load small piceces of files containing the sound of instruments such as Drums or cymbals. These small samples of user defined sounds can be played in any order to produce the music of an orchestra.

Many software synthesizers also support MIDI which is a standard method for communicating with synthesizers. More on MIDI later.

Software synthesizers can run stand alone or as plugins with other applications. You can program, control, compose melody all using the soft synths.
Picture on left shows a softsynth.

Polyphonic Synthesizers
Synthesizers which can play more than one note at a time of the same voice (instrument) are called polyphonic synthesizers. It does not mean that a device can play multiple instruments together. You might have heard of polyphonic ring tones. Polyphony gives a rich quality to the sound and resembles like an orchestra concert. For example a guitar chord sound is polyphonic because it involves many strings to be plucked together at once.
A polyphonic synthesizer would be able to generate a guitar chord kind of sound because it can produce sound for each plucked string together. Most of the standard synthesizers (whether hardware or software) available today are polyphonic. Few cheap once available in the market a monophonic and they don’t sound good.

Multitimberal Synthesizer –

Synthesizers which can play sound of more than one instrument together are called Multitimberal Synthesizer. For example on such synthesizers you can play a piano and violin sound together. To control two instruments together it needs to provide two keyboards which may not be easy. Few synthesizers offer the ability to split the keys of the keyboard in two section. Each section then maps to one instrument which can be played by a single user simultaneously.

Patches/Soundbank -
The different sounds that a synthesizer or sound generator can produce are sometimes called "patches". Programmable synthesizers commonly assign "program numbers" (or patch numbers) to each sound. For instance, a sound module might use patch number 1 for its acoustic piano sound, and patch number 36 for its fretless bass sound. The association of all patch numbers to all sounds is often referred to as a patch map. Usually one patch corresponds to one instrument sound like piano or accrodian. A collection of patches is called a soundbank.