Parameters that affect the quality of digital audio. (Part 2)
The format is also called the number of channels in multichannel sound systems (5.1; 7.1). Initially such a system was developed for cinemas but later spread by Software Codec
Software-level audio codec
§ G.723.1 – one of the basic codecs for IP telephony applications
§ G.729 – proprietary narrowband codec used for digital representation of speech
§ Internet Low Bit Rate Codec (iLBC) – a popular free codec for IP telephony (in particular for Skype and Google Talk)
Audio Codec (Audio Codec; Audio Encoder / Decoder) – A computer program or hardware designed to encode or decode audio data.
Software codec
A software-level audio codec is a specialized computer program, a codec that compresses (compresses) or decompresses (decompresses) digital audio data according to an audio file format or streaming audio format. The task of an audio codec as a compressor is to provide an audio signal with a certain quality / precision and the smallest possible size. Compression reduces the amount of space required to store audio data, and it is also possible to reduce the bandwidth of the channel through which the audio data is transmitted. Most audio codecs are implemented as software libraries that interact with one or more audio players such as QuickTime Player, XMMS, Winamp, VLC media player, MPlayer, or Windows Media Player.
Popular software audio codecs by application:
§ MPEG-1 Layer III (MP3) is a proprietary audio recording codec (music, audiobooks, etc.) for computer equipment and digital players
§ Ogg Vorbis (OGG) – the second most popular format, widely used in computer games and file-sharing networks to transfer music
§ GSM-FR is the first digital voice coding standard used in GSM phones
Adaptive Multispeed (AMR): human voice recording on mobile phones and other mobile devices
Dependence of the loudness, as well as the tone of the sound on the intensity and frequency of the sound wave.
Hertz (denoted by Hz or Hz) is a unit of measurement for the frequency of periodic processes (eg, oscillations).
1 Hz means an execution of said process in one second: 1 Hz = 1 / s.
If we have 10 Hz, this means that we have ten executions of said process in one second.
The human ear can perceive sound at frequencies ranging from 20 vibrations per second (20 Hertz, low sound) to 20,000 vibrations per second (20 KHz, high sound).
In addition, a person can perceive sound in a wide range of intensities, in which the maximum intensity is 1014 times greater than the minimum (one hundred thousand billion times).
To measure the volume of sound, a special unit of “decibels” (dB) was invented and used.
A decrease or increase in sound volume by 10 dB corresponds to a decrease or increase in sound intensity by 10 times.
Sound volume in decibels
In order for computer systems to process sound, a continuous audio signal must be converted to a discrete digital form by time sampling.
For this, a continuous sound wave is divided into separate small time sections, for each section a certain value of sound intensity is set.
Therefore, the continuous dependence of the loudness of the sound at time A (t) is replaced by a discrete sequence of loudness levels. On the graph, this appears to replace a smooth curve with a sequence of “steps.”
Sync Audio Sampling
A microphone connected to the sound card is used to record analog audio and convert it to digital format.
The denser the discrete fringes are located on the graph, the better it is ultimately possible to recreate the original sound.
