The audio signal is an analog signal that is electrically correct for an audio signal. The frequency range normally heard by humans is between 20 and 20,000 Hz, approximately equivalent, almost at 10 octaves.
A digital audio file is a sound or sound sequence that has been converted into a digital format for storage on a computer. We can distinguish 3 general types of audio formats:
It stores information as it is captured by a microphone, it stores the amplitude and frequency of the sound in a certain time period.
This time frame is known as the sampling rate of the audio file and is usually measured in the number of samples taken from what the microphone listens every second. The general values are 11000 Hz, 22000 Hz, and 44000 Hz. The higher this number, the better the sound quality. The most commonly used formats on the network are waveforms.
They save the notes by reading them from a kind of MIDI input (Music Instrument Digital Interphase). Some channels are recorded and placed on specific channels.
It is left to the computer and an international standard that defines how each channel is played. The typical example is exactly MIDI.
They initially store an example of how each channel will sound, similar to the sound waveforms, and then record a series of notes for each channel.
A typical example of this format is MOD, which works precisely on several systems due to its ability to produce excellent sound quality and also takes up very little disk space when stored.
Audio files have different formats depending on which tools or applications and for what purpose they are created. When working with a specific application, the software assigns an extension depending on the type of file created so that it can be identified later.
While some allow the video to play, the main audio formats are:
Audio Interchange File Format (AIFF) – .Aif (F) and .Snd Extensions
AIFF, created by Apple, is used on Mac computers and multimedia applications but is not very common on the Web.
Audio for Unix (AU) – Au, uLaw and MuLaw Extension
It is a very popular format for uncompressed samples created by the Sun company. It is one of the oldest on the Internet, especially on Unix platforms.
Audio-Video Interleaved (AVI)
AVI was created by Microsoft. It is not a format in itself, but an audio/video container. You must have installed the codecs and the Windows player to view them.
The files created by Macromedia are DIR files with .ir and .dxr extensions.
MIDI (Music Instrument Digital Interface) – .Mid Extension
Such files are created using PC synthesizers. MIDI files represent notes and other sequence information so music can be synthesized.
MOD – .Mod and .Dxr Extensions
This format originated from Amiga platforms created by Commodore. Another form of format for reproducing digital modules. Like MIDI, S3M, FAR, or MTM, all these formats include the music model and a number of samples so that the music of the model can be played with the appropriate instrument.
MPEG Audio was created by MPEG (Motion Pictures Experts Groups). This is an audio compression format standard that designs 3 different coding-decoding levels of the audio signal.
Audio and Media Players
To read different types of audio formats, you need a player with plug-ins or programs that play audio and usually allow listening from major web browsers such as Internet Explorer or Google Chrome.
In the case of MP3, in addition to the computer, we can listen to songs and sounds in MP3 format with an MP3 player program, on other devices independent from the computer, with a specially designed portable device or another player, which supports the reading and reproduction of such files.
Today, many DVD or DTV players (Digital TV) have the option that can be combined with the Dolby Digital surround sound system. This option is even available on mobile phones.
Digital audio is measured by the sampling frequency, that is, you need to measure the number of times that the sound has been digitized over a period of time.
Sampling rates are specified in kilohertz (kHz), which indicates the number of times the sound is sampled per second. For example, CD sound quality is achieved at 44.1 kHz or 44,100 samples per second.
In the case of stereo sound, two 8-bit channels are required; When there are 16 bits per sample, this results in 705,600 bits of data from a CD, producing high-quality sound. If we were to transmit sound over the network in this way, the transmission of this enormous amount of data would take up almost half the network’s bandwidth.
Since average web users do not have a bandwidth size, it is necessary to reduce the sampling frequency to create a digital sound that can be sent over the web.
8 kHz mono sampling rate gives good results for simple applications such as spoken language. Note that the playback hardware usually consists of a simple sound card and a small speaker.
Low-quality sound does not require more than 64,000 bits of data per second, but the user needs to wait for the download of the sound, and continuous sound is almost impossible.
Audio CDs, such as DAT (data) systems, use digitization of the signal using one of the simplest coding formats and PCM (Pulse Code Modulation) or encoded pulse modulation, which is widely used on the phone.
However, most of the sound information stored by these coding systems can be discarded because the human ear cannot detect certain frequencies called a certain critical band.
Digitization adds noise to the signal, and to avoid this, it is necessary to use a larger number of bits in sampling and quantization, which is the 2 stages in which a digitization process is created.
Frequencies up to 44.1 kHz in CD state and 48 kHz in DAT state are used to achieve the high quality sound. Regarding quantization, the more bits are used, the better the resolution.
At 44.1 kHz and using 16 bits (Hi-Fi Audio) to measure the signal, one of the two channels on the CD generates more than 700 kbit/s.
It should be noted that the first music CD was released in 1982 and the players were commercialized in the same year, so digital audio has a short development period and there is the possibility of listening to music or sound even more clearly. The main digital audio supports are:
CD-A (Compact Disc Audio)
This is a very high-quality sound in digital media and relies on a digital recording without further processing, that is, all information produced in the recording is stored on a compact disk without compression.
On a normal 650 Mb CD, this gives us a maximum time of about 74 minutes per CD, so it fits all the information contained in the long-awaited vinyl records or LPs.
CD-R (Recordable Compact Disc)
Stands is a blank CD that does not support rewriting.
CD-RW (Rewritable Compact Disk)
It is an empty compact disc that supports rewriting.
HDCD (High Definition Compatible Digital)
High Definition Definition Digital, developed by Pacific Microsonics for the development of standard audio CDs, is an audio encoding process.
With the introduction of new audio formats such as SACD and DVD Audio, the life cycle was short.
SACD (Super Audio Compact Disk)
It is a high definition audio format in CD media introduced by Sony and Philips, which uses SDS or Direct Stream Digital system to produce digital signals. Traditional stereo information can be recorded on CD, but there is room for additional channel information to be included.
It is a high definition audio format that works with 24-bit resolution on DVD and 192 kHz sampling rate far above 16 k/44 kHz CD Audio.
VCD (Video Compact Disc)
It is a video format that is much lower in performance and quality than DVD but is widely applied in CD media.