P2 Understand the methods and principles of sound design and production.
Exercise 1
Research and explain when you would use the following sound formats and why?
Sound file formats
Uncompressed
wav File
The WAV file one of the simplest digital audio file formats. Microsoft and IBM originally developed WAV in 1991 for the use within Windows 3.1. Remember the first time you heard your PC making ‘chime’ noises, and not just beeps? Well, that’s courtesy of the WAV file.Without getting too geeky, the WAV was derived from the RIFF (resource interchange file format), which stored data in indexed chunks (interesting, eh?). Apple derived its own version of this file format in 1988: AIFF. Essentially, AIFFs are the apple equivalent of WAVs.
They work by taking an audio signal and converting it to binary data. To do this, a device called an analogue to digital converter (AD) takes snapshot ‘slices’ thousands of times per second. For example, CD quality audio records at 44.1kHz, meaning it records at 44,100 slices per second. This makes it capable of recording the entire audible frequency range of 20hz-20khz.
aiff File
The aiff is a file extension for an Audio Interchange File format. AIF is an audio format used by Silicon Graphics and Macintosh applications.In Windows, the extension for this file type is usually AIF. On a Mac, the file extension is not needed but when present may be AIFF. A Mac file uses a Type and Creator resource to identify itself to the operating system and the applications that can open it.
AIFF is one of the two most common audio file formats used in the Apple Macintosho perating system. The other is Sound Designer II (SDII). Most CD writers can accept AIFF or SDII files interchangeably when writing a Red Book audio CD. AIFF is sometimes referred to as "Apple Interchange File Format."
An AIF file contains the raw audio data, channel information (monophonic or stereophonic), bit depth,sample rate, and application-specific data areas. The application-specific data areas let different applications add information to the file header that remains there even if the file is opened and processed by another application.
MIME type: audio/aiff, audio/x-aiff, sound/aiff, audio/rmf, audio/x-rmf, audio/x-pn-aiff, audio/x-gsm, audio/mid, audio/x-midi, audio/vnd.qcelp
au File
(AUdio file) A digital audio file format from Sun that is used on the Internet and can be played by a Java program. It provides toll-quality sound and uses the .AU extension. It generally uses the u-Law (mu-Law) encoding method, and raw u-Law files and AU files are the same except for the file header.smp File
The smp file extension is associated with AutoCAD Civil Building Information Modeling (BIM) software for civil engineering design and documentation, developed by Autodesk.
The smp file stores sampled station list.
voc File
Files that contain the .voc file extension are most commonly associated with Creative Labs audio hardware devices. The VOC files contain audio files that are used by the associated Creative Labs hardware.VOC files can contain audio clips, music files, instrument sounds and sound effects that are used with the associated hardware device. The VOC file format is a compressed file format, allowing for a reduction in the size of the audio file that is stored on the user's hard drive.
The Quartet software application has also been known to use the .voc file suffix for similar purposes. These VOC files contain audio files that are used by the Quartet program.
The .voc file format is also used by the ZX Spectrum software application. These VOC files contain tape image files that are created with the ZX Spectrum software.
Lossy compression
mp3 File
MP3 (MPEG-1 Audio Layer-3) is a standard technology and format for compressing a sound sequence into a very small file (about one-twelfth the size of the original file) while preserving the original level of sound quality when it is played. MP3 provides near CD quality audio.ra File
RA is a file extension for a streaming audio file format used by RealNetworks' RealPlayer. An RA file generally contains audio data encoded in the proprietary RealAudio codec.vox File
Dialogic ADPCM or VOX is an audio file format, optimized for storing digitized voice data at a low sampling rate. VOX files are most commonly found in telephony applications, as well as an occasional arcade redemption game.Audio Sampling
How can resolution and bit-depth constrain file size?In digital audio using pulse-code modulation (PCM), bit depth is the number of bits of information in each sample, and it directly corresponds to the resolution of each sample. Examples of bit depth include Compact Disc Digital Audio, which uses 16 bits per sample, and DVD-Audio and Blu-ray Disc which can support up to 24 bits per sample.
In basic implementations, variations in bit depth primarily affect the noise level from quantization error—thus the signal-to-noise ratio (SNR) and dynamic range. However, techniques such as dithering, noise shaping and oversampling mitigate these effects without changing the bit depth. Bit depth also affects bit rate and file size.
Bit depth is only meaningful in reference to a PCM digital signal. Non-PCM formats, such as lossy compression formats, do not have associated bit depths. For example, in MP3, quantization is performed on PCM samples that have been transformed into the frequency domain.
Explain what the following words mean:
Sample rate -Sample rate is the number of samples of audio carried per second, measured in Hz or kHz (one kHz being 1 000 Hz). For example, 44 100samples per second can be expressed as either 44 100 Hz, or 44.1 kHz. Bandwidth is the difference between the highest and lowest frequencies carried in an audio stream
Mono-Mono uses one, stereo uses more than one. In monaural sound one single channel is used. It can be reproduced through several speakers, but all speakers are still reproducing the same copy of the signal. In stereophonic sound more channels are used (typically two).
Stereo-This is usually achieved by using two or more independent audio channels through a configuration of two or more loudspeakers (or stereo headphones) in such a way as to create the impression of sound heard from various directions, as in natural hearing.
Surround-Surround sound is a term used to describe a type of audio output in which the sound appears to "surround the listener" by 360 degrees. Surround sound systems use three or more channels and speakers in front and behind the listener to create a surrounding envelope of sound and directional audio sources. The term surround sound has become popular in recent years and more commonly used since the advent of home theater systems. Surround sound can be either an analog or digital system.
Audio Limitations of Games Platforms
DSP – Digital Signal ProcessorRAM – Random Access Memory.
A digital signal processor DSP is a specialized microprocessor or a SIP block, with its architecture optimized for the operational needs of digital signal processing. The goal of DSPs is usually to measure, filter and/or compress continuous real-world analog signals.
File format (eg Mp3, Wav, Aiff)-Limitations
Unlike a bitmap image, a vector image is incapable of reproducing a continuous tone photographic image,Vector images tend to produce an unrealistic image and a more cartoon looking image.
Because a vector file has to load vector software and then open and calculate file paths it can be slow in opening therefore may be unsuited.Audio output (eg Mono, Stereo, Surround)
PCM –Pulse Code Modulation
Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, Compact Discs, digital telephony and other digital audio applications.
