Keywords Sample Frequency The number of audio samples

Keywords Sample Frequency - The number of audio samples captured every second Sample Size / Bit Depth - Number of bits available for each sample Bit Rate -The number of bits used per second of audio Data Representation Sound

Digital Audio Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. Sound exists as waves – however as computers only understand binary values this needs to be converted into such. Sounds created on a computer exist as digital information that is encoded as audio files. Digital sound is broken down into thousands of samples per second – each of these samples is then stored as binary data. The quality that the samples are stored with depends on different factors: Sample Frequency Sample Size Bit Depth Bit Rate

Sample Size/Bit Depth Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. Bit depth is the number of bits available for each sample. The higher the bit depth, the higher the quality of the audio. Bit depth is usually 16 bits on a CD and 24 bits on a DVD. Bit depth of 16 has a resolution of 65, 536 possible values. Bit depth of 24 has over 16 million possible values. 16 -bit resolution means each sample can be any binary value between 0000 and 1111. 24 bit means the maximum binary number is 1111 1111 which creates 16, 777, 215 possible values.

Sample Rate Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. The sample rate is how many samples, or measurements, of the sound are taken each second. The more samples that are taken, the more detail about where the waves the higher the quality of the audio. Also, the shape of the sound wave is captured more accurately. Each sample represents the amplitude of the digital signal at a specific point in time. The amplitude is stored as either an integer or a floating point number and encoded as a binary number.

Sample Rate Example Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. Common audio sample rate for music is 44, 100 samples per second (CDs) – the unit this is measured in is hertz – This is 44, 100 hertz or 44. 1 kilohertz (k. Hz). Telephone networks and VOIP services use a sample rate as low as 8 k. Hz.

Sample Rate Objectives This refers to the amount of samples taken. The higher the sample frequency the more accurate it represents the true sound wave, ALTHOUGH it increases the size of the file. ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. Low sample rate. High sample rate.

Bit Rate The bit rate of a file tells us how many bits of data are processed every second. Bit rates are usually measured in kilobits per second (kbps). Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. How do you Calculate bit rate? The bit rate is calculated using the formula: Frequency × bit depth × channels = bit rate A typical, uncompressed high-quality audio file has a sample rate of 44, 100 samples per second, a bit depth (the number of bits available for each sample) of 16 bits per sample and 2 channels of stereo audio. The bit rate for this file would be: 44, 100 samples per second × 16 bits per sample × 2 channels = 1, 411, 200 bits per second (or 1, 411. 2 kbps) A four-minute (240 second) song at this bit rate would create a file size of: 14, 411, 200 × 240 = 338, 688, 000 bits (or 40. 37 megabytes)

Audio as Binary Audio file is inputted through a microphone and broken down into thousands of samples per second, Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. The more samples recorded per second the higher the quality of the audio file, but the more memory it will consume. Each sound sample is stored as Binary Data. The more bits per sample also increases the higher the quality of the audio, on a CD the bit depth is usually 16 bits The bit rate of a file tells us how many bits of data are processed every second are usually measured in Kilobytes per second (kbps) Frequency x bit depth x channels = bit rate The more samples recorded per second the higher the quality of the audio file, but the more memory it will consume.

Questions 1. What are three factors that affect the size of a sound file? Objectives ADVANCED: Understand how sound can be stored in digital form. EXPERT: Understand what factors can affect the size of a sound file and quality of feedback. 2. Explain how the three factors affect the size of a sound file and the quality of the playback? 3. Explain how file compression could be used so that high quality audio files stay of a high quality?