Sound

There are two types of Audio recordings Analog and Digital Audio. Digital audio involves capturing the sound waves through an analog interface and the other is via a MIDI interface - Musical Instrument
Digital Interface.

In Digital Audio there are three sampling frequencies that are often used which include, 44.1kHz, 22.05kHz and 11.025kHz. The higher the bit rate the higher the quality of the clip.

Digital Audio resolution determines the accuracy with which sound can be digitized. Size of a monophonic digital recording = sampling rate x (bit resolution / 8) x 1.

Size of a stereo recording = sampling rate x duration of recording in seconds x (bit resolution/8) x 2.

Exam - Calculating CD Audio quality. 

Steps - 1 x 2 x 44.100 x (16/8) = 176, 400 Bytes / 1024.
    So -  172 KB's for one second.

One minute would be - 10, 336 KB - 10.1MB.

 Analogue to Digital (and Back)

• Soundwaves we hear are analogue. The Computer stores data only in digital form (numbers computer code)

The process of converting between analogue and digital involve using a sound card interface usually built into your computer motherboard.

An audio files is created by sampling a sound and recording the amplitude of the wave at periodic intervals along the waveform.

Effects of Digital Sampling

The reconstructed wave is not an exact replica of the sampled wave.

Digitalization Process (1) -  The first step is to measure the amplitude as set intervals (Sample Frequency)

Key Concept

Computers store all information in a binary digital form, which means all data - text, photographs, audio or whatever else - is comprised of collections of ones and zeroes. The fundamentals building block do digital audio is binary numbers.

4 Steps in the Digitalization process; 1. Sampling a sound (from the analogue sound wave), 2. Recording the amplitude of each sample, 3. Store each record sequentially in a digital file, 4. Reconstruct the waveform from the digital file.

MP3 (MPEG-1 Audio Layer-3) 

This is the most common form of compress sound sequence into a small file. An MP3 format file will be 1/10 1 /112 the size of the standard wave format file from which it was derived.

MP3 format preserves the original level of sound quality when it is played (reconstructed).

Ideal for web, Samaller file size -> Less time to download. 

Copyright issues!

Midi AUDIO (Musical Instrument Digital Interface)

Enables computers and digital instruments to create sound from scratch. A sequence of software and sound synthesizer is required in order to create MIDI scores.

Since they are small, MIDI files embedded in web pages load and play promptly.

Which is better? Analogue or Digital? Neither is best. There are pros and cons of both. All depends on it's application, is it for web, dvd, cd etc.

With Midi, it is difficult to playback spoken dialog, while digitized audio can do so with ease.