MAIN AUDIO FORMATS
Even the audio formats differ in their versatility and level of compression, and even if they are not as numerous as the video formats, it is better to look at the properties to get satisfactory results according to the requirements of our work.
Microsoft Wave [Extension: WAV] It is Microsoft’s proprietary format and is certainly the most widely used. This diffusion depends on commercial aspects and the fact that it is the most supported among the competitors. It has various compressions and is a versatile and highly editable format. For this reason, it is suitable for general digital audio, both for multimedia publications (although there are certainly better formats) and for desktop video (real standard). An excellent program for processing wave files (but also other formats) is CoolEdit.
MPEG Audio (extension: MPG / MP3) MP3 stands for MPEG1 Layer3. The MPEG algorithm, the basis of MP3, emerged from the need to develop a world standard for the representation of moving images and audio. This standard was developed in 1988 for the treatment of audio and video signals and has the special feature of compressing files and reducing them by 12 times compared to their natural size.
This high-compression format is based in particular on theories of psychoacoustics: each individual has a hearing that is sensitive to frequencies from 20 Hz to 20 kHz, and in particular the man perceives sounds between 2 and 4 kHz better. In addition, some sounds mask nearby frequencies so that you cannot hear all of the sounds.
These considerations have led to the development of an algorithm that eliminates all “redundant” noise for the human ear and achieves a high level of file compression and sound quality that is comparable to the digital and can be downloaded directly to your PC.
MP3 enables good results, making small and high quality playback compatible. An established audio standard is the MPEG Layer3 version, which produces very small files of excellent quality, an excellent compromise when duplicating and creating audio files on CD. The XingMPEG encoder is an excellent software for creating MP3s.
Given the prevalence and importance of the topic on a legal level, let’s find out what it is and what benefits we can achieve by using this MPEG format.
An audio CD generally contains 60 to 78 minutes and is characterized by a quantization level of 16 bits and a sampling rate of 44.1 kHz, ie 44,100 samples per second. The quantization level describes the maximum number of intensity levels that a single sample can hold: for example 8 bits = 256 levels (28), 16 bits = 65,356 levels (216). The higher the number of levels that the signal can assume, the more precise the signal reproduction.
There is approximately 650 MB of data on a normal audio CD.
Conventionally, to reduce the size, we can work in two ways: 1) Reduce the quantization: that is, convert the samples from 16 bits to 8 bits, but lose the dynamics, quality and get a lot of noise; 2) Reduce the sampling frequency. As a result, the frequency range would decrease in the event of a loss of resolution.
The MPEG format, on the other hand, reduces the amount of information stored and therefore significantly reduces the size of the files by filtering out unimportant audio information according to the models developed on this basis. From research on the perception of the human ear, you decide which information is important and which is not . These studies have enabled us to know how our brain analyzes sounds, except irrelevant ones that are imperceptible (e.g. ultrasound).
The MPEG audio format also performs this process of removing intelligent weak signals. So if there is a strong signal, the weakest signal is not perceived.
When using a high compression rate, the MPEG encoder eliminates parts of audible information that are still of minor importance. With a slight compression rate, the difference to the uncompressed original is minimal.
Layers I, II, III can be viewed as the layers through which the MPEG format has evolved. All layers are based on the same perceptual coding scheme, the complexity of which increases for each of them. Layer II has superior quality at lower bit rates than Layer I; However, the most complex coding system currently available is Layer III,
MP4 (Extension: MP4) is an audio compression technology recently launched by Global Music Outlet (GMO) under license from AT&T Labs (January 99). As you understand, it is a further development of the MP3 format and seems to offer the ability to offer it a higher compression factor, which should even reach a factor of 16. Although the name is very similar, conceptually it has nothing to do with layer 3 and is actually in direct competition with it. Compressed MP4 files are presented as executable Win9x or WinNT files and offer the relatively encapsulated player.
Audio exchange (extension: AIF / AIFF) Format created to standardize the various audio standards between PC and Machintosh.
Microsoft NetShow (Extension: ASF) Audio extension of the format for streaming audio / video on the web.
Yamaha SoundVQ [Extension: VQF] Audio format released by Yamaha in direct competition with MP3.
