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Presentation on the topic: Audio encoding

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Analogue and discrete methods of sound representation Sound is a physical phenomenon representing the propagation of mechanical vibrations in the form of elastic waves in a solid, liquid or gaseous medium. With an analog representation, a physical quantity takes on an infinite number of values, and its values ​​change continuously. In analog form, sound is a wave, which is characterized by: The pitch of the sound is determined by the frequency of vibration of the vibrating body. The loudness of sound is determined by the energy of vibrational movements, that is, the amplitude of vibrations. The duration of the sound is the duration of the vibrations. The timbre of sound is the color of sound.

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Discrete Representation of a Sound Wave In the process of encoding a continuous sound signal, its temporal sampling is performed. A continuous sound wave is divided into separate small time sections, and for each such section a certain amplitude value is set. With a discrete representation, a physical quantity takes on a finite set of values, and its value changes abruptly.

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The quality of encoding audio information depends on: Sampling frequency, i.e. the number of measurements of the signal level per unit of time. The more measurements are made in 1 second (the higher the sampling rate), the more accurate the binary encoding procedure. The sampling frequency is measured in Hz - the unit of measurement for the frequency of periodic processes is 1 Hz = 1 / s

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Audio Encoding Depth Encoding depth is the amount of information needed to encode discrete loudness levels of digital audio. N = 2i where N is the number of digital audio volume levels where i is the audio coding depth. Modern sound cards provide 16-bit audio encoding depth. Quantity various levels signal (states for this encoding) can be calculated by the formula: N = 2i = 216 = 65536. In the process of encoding, each sound volume level is assigned its own 16-bit binary code, the code 0000000000000000 will correspond to the lowest sound level, and 1111111111111111 to the highest sound level.

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Quality of digitized audio The higher the sampling rate and encoding depth of the audio, the better the quality of the digitized audio will be and the better you can approximate the digitized audio to the original sound. The highest quality of digitized sound, corresponding to the quality of an audio CD, is achieved with a sampling rate of 48,000 times per second, a sampling depth of 16 bits and recording of two audio tracks (stereo mode). It must be remembered that the higher the quality of digital sound, the greater the information volume of the sound file.

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Sound editors Sound editors allow you not only to record and play sound, but also to edit it. The most prominent can be safely called, such as Sony Sound Forge, Adobe Audition, GoldWave and others. Digitized sound is presented in sound editors in a clear visual form, so the operations of copying, moving and deleting parts of an audio track can be easily performed using a computer mouse. In addition, you can overlay, overlap audio tracks on top of each other (mix sounds) and apply various acoustic effects (echo, reverse playback, etc.). Sound editors allow you to change the quality of digital sound and the volume of the final sound file by changing the sampling rate and encoding depth. Digitized audio can be saved uncompressed as audio files in universal WAV format (Microsoft's format) or in OGG, MP3 (lossy) compressed formats.

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Properties: sound - longitudinal wave; spreads in elastic media (air, water, various metals, etc.); has a finite speed. Sound vibrations (waves) are mechanical vibrations whose frequency ranges from 20 to 20,000 Hz. Sound vibrations 20 Hz 20,000 Hz

the loudness of the sound depends on the amplitude of the vibrations. The larger the vibration amplitude, the louder the sound. The pitch of the sound is determined by the frequency of the vibrations in the air. the speed of sound is the speed of wave propagation in the medium. sound timbre - sound coloring depending on the sound source (violin, piano, guitar, etc.). The unit of sound loudness is the decibel (dB) (a tenth of a bela). Named after Alexander Graham Bell, inventor of the telephone. sound_high_low.swf sound_quiet_aloud.swf

fourth.swf third.swf Dependence of the volume and pitch of the sound on the intensity and frequency of the sound wave

Sound source Level (dB) Calm breathing Not perceived Whispering 10 Rustling of leaves 17 Leafing through newspapers 20 Normal house noise 40 Surf on the beach 40 Medium conversation 50 Loud conversation 70 Vacuum cleaner 80 Subway train 80 Rock concert 100 Thunder 110 Jet engine 110 Shot from a gun 120 Pain threshold 120

Audio information 2. Audio temporal scoring 3. Sampling frequency 4. Audio coding depth 5. Quality of digitized audio 6. Sound editors

Analog Discrete physical quantity takes on an infinite number of values, and they change continuously. a physical quantity takes on a finite set of values, and they change stepwise. Vinyl record (soundtrack changes its shape continuously) Audio CD (soundtrack contains areas of varying reflectivity)

t A(t) Temporal sampling is the division of a continuous sound wave into separate small time sections, and for each section a certain amplitude value is set.

QUANTIZATION - the process of replacing real signal values ​​with approximate ones with a certain accuracy. BITREYT (bitrate) - the level of quantization, the amount of information per unit of time (bits per second). That is, how much information about each second of the recording we can spend. Measured in bits (bit).

Audio information is stored as amplitude values ​​taken at specific times (i.e. measurements are taken in "pulses").

To digitize sound, special devices are used: an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC).

Let the sound encoding depth be 16 bits, then the number of sound volume levels is: N = 2 I = 2 16 = 65 536 - 1111111111111111. AUDIO SAMPLING DEPTH (I) is the amount of information needed to encode discrete digital sound volume levels. N - number of volume levels I - coding depth

AUDIO SAMPLING FREQUENCY is the number of measurements of sound volume in one second. 1 Hz = 1 / s 1 kHz = 1000 / s Samplerate (samplerate) - sampling frequency (or sampling frequency) - the sampling frequency of a signal continuous in time during its sampling (in particular, by an analog-to-digital converter - ADC). sound_frequency.swf

The higher the quality of digital sound, the greater the information volume of the sound file. Parameter Encoding depth Sampling frequency Telephony 8 bit to 8 kHz Medium quality 8 bit or 16 bit 8-48 kHz CD audio 16 bit to 48 kHz

V = I * M * t * k V - audio file volume, I - audio encoding depth, M - audio sampling frequency, t - file audio duration, k - number of audio channels (mono mode k = 1, stereo k = 2)

Example. Estimate the information volume of a high-quality stereo audio file with a duration of 1 minute, if the "depth" of encoding is 16 bits, and the sampling frequency is 48 kHz. The information volume of a sound file with a duration of 1 second is: 16 bits * 48,000 * 2 = 1,536,000 bits = 187.5 KB This means that the bit rate or playback speed should be 187.5 kilobytes per second. The information volume of a sound file with a duration of 1 minute is: 187.5 Kb / s * 60 s = 11 Mb

Noise Removal Splitting a stereo recording into two different files: Audio mixing Applying effects Sound editing is any kind of transformation.

Sound editors allow you to change the quality of digital audio and the size of the audio file by changing the sampling rate and encoding depth. Digitized audio can be saved uncompressed as universal WAV or compressed MP3 audio files. When saving sound in compressed formats, sound frequencies with low intensity that are "excessive" for human perception and coincide in time with sound frequencies with high intensity are discarded. The use of this format allows you to compress audio files dozens of times, but leads to irreversible loss of information (files cannot be restored in their original form).

WAVE (.wav) is the most widely used format. Used in Windows to store sound files. MPEG-3 (.mp3) is the most popular audio file format today. MIDI (.mid) - do not contain the sound itself, but only commands for playing the sound. The sound is synthesized using FM or WT synthesis. Real Audio (.ra, .ram) - designed to play sound on the Internet in real time. MOD (.mod) is a music format that stores digitized sound samples that can then be used as templates for individual notes.

Editing area Timeline Main menu Toolbars http://www.audacity.ru/p1aa1.html

Learn the abstract, solve problems in the notebook. Audio Coding Tasks Level 5 Determine the length of an audio file that will fit on a 3.5” floppy disk. Please note that 2847 sectors of 512 bytes are allocated for data storage on such a diskette. a) with low sound quality: mono, 8 bits, 8 kHz; b) with high sound quality: stereo, 16 bit, 48 kHz. Level "4" The user has a memory of 2.6 MB. You need to record a digital audio file with a duration of 1 minute. What should be the sampling rate and bit depth? Level 3 Specify the amount of storage space for a digital audio file that has a playing time of two minutes at a sampling rate of 44.1 kHz and a resolution of 16 bits.

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Since the beginning of the 90s, PCs have been able to work with sound information. Every PC with a sound card, microphone, headphones or speakers can record, store and play sound information. * We work with graphic information through graphic editors, then with sound information using audio file editors. We work with graphic information through graphic editors, then with sound information using audio file editors.

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Sound information Sound is a wave propagating in air, water or other medium with continuously changing intensity and frequency. *

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In the process of encoding audio information, temporal sampling occurs when the sound wave is broken into separate small time sections. For each such area, a certain value of sound intensity is set. At the end of the sampling process, audio information is stored in the computer's memory in the form of binary codes. *

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With the help of a microphone, the sound is converted into electric current oscillations, which have a certain amplitude. A sampling device (ADC) measures electrical voltage in a certain range and converts the numerical value of the voltage into a multi-bit binary number. Reverse process: DAC converts binary numbers into electrical voltage. The step signal received at the output of the DAC is converted into sound using an amplifier and a speaker. * Audio information processing devices

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There are two parameters that affect the quality of audio reproduction: the sampling rate and the audio encoding depth. The audio encoding depth is the size of the cell allocated for recording the value of the amplitude (loudness) in the binary code. Modern sound cards can encode 65536 different signal levels or states (65536=2i, i=16 bits). Thus, modern sound cards provide 16-bit audio encoding (coding depth). With each sample, the value of the amplitude of the audio signal is assigned a 16-bit code. * Sound information options

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The sampling rate is the number of sound volume measurements made by the instrument in 1 second. Frequency is measured in hertz (Hz). One measurement per second corresponds to a frequency of 1 Hz. 1000 measurements in one second - 1 kilohertz (kHz). The number of samples per second can be in the range from 8000 to 48000, i.e. the sampling rate of the analog audio signal can take values ​​from 8 to 48 kHz. *

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The human ear perceives sound at frequencies ranging from 20 vibrations per second (low sound) to 20,000 vibrations per second (high sound). The higher the frequency and sampling depth of the sound, the better the quality of the digitized sound will be. The lowest quality of digitized audio corresponding to the quality telephone communication is obtained at a sampling rate of 8000 times per second, sampling depth of 8 bits and recording of one sound track ("mono" mode). *

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The highest quality of digitized sound, corresponding to the quality of an audio CD, is achieved with a sampling rate of 48,000 times per second, a coding depth of 16 bits, and recording of two audio tracks (stereo mode). *

Coding and processing of sound information

Sound is a wave with a continuously changing amplitude and frequency.

The greater the amplitude, the louder the sound The greater the frequency, the greater the tone

Sound
Volume in
decibels
lower limit
sensitivity
human ear
0
rustle of leaves
10
Talk
60
car horn
90
Jet engine
120
pain threshold
140

In order for a computer to process sound, a continuous audio signal must be converted to digital discrete form using

In order for the computer to
process sound,
continuous beep
should be converted to
digital discrete form
with the help of a temporary
discretization

Temporal Audio Sampling

A(t)
Temporal Audio Sampling
t

The quality of the received digital sound depends on the number of measurements of the sound volume level per unit of time, i.e., the sampling frequency

Received digital sound quality
depends on the number of level measurements
sound volume per unit time, i.e.
sample rate.
The more measurements
produced in 1 second (the more
sampling rate), the more accurate
digital audio ladder
follows the curve of the dialog signal.

Digital audio characteristics: 1. frequency 2. depth

The audio sample rate is the number of times the volume of a sound is measured in one second.

The audio sampling rate can range from 8,000 to 48,000 sound volume measurements per second. (Hz)

Audio encoding depth (i) is the amount of information needed to encode discrete digital audio loudness levels

Audio encoding depth
(i) is the quantity
information that
needed for coding
discrete levels
digital audio volume.

If the encoding depth is known, then the number of digital sound volume levels can be calculated by the formula N = 2i, where i is the encoding depth

If the encoding depth is known,
then the number of volume levels
digital sound can be calculated
i
according to the formula N = 2,
where i is the encoding depth and
N - number of digital sound volume levels
Let the audio encoding depth
is 16 bits, then
number of sound volume levels
equals:
N = 2i = 216 = 65536.

Quality of digitized sound

The higher the frequency and
audio sampling depth,
the more quality
will sound
digitized sound

Sound editors allow you not only to record and play sound, but also to edit it

Sound editors allow you to change the quality of digital sound and the size of the sound file by changing the sampling rate and depth to

Sound editors allow
change the quality of digital
sound and volume of sound file
by changing the frequency
discretization and depth
coding. Digitized audio
can be saved without compression
sound files in
universal WAV format
or in compressed MP3 format.

The lowest quality of digitized audio, corresponding to the quality of telephone communication, is obtained at a sampling rate of 8000 times per second

The lowest quality of digitized sound,
corresponding to the quality of telephone communication,
obtained at a sampling rate of 8000
times per second, sampling depth 8 bits and
recording one sound track (mono mode).
The highest quality digitized sound,
corresponding
quality
audio CD,
achieved at a sampling rate of 48,000
once per second, sampling depth 16 bits
and recording two audio tracks (mode
"stereo").

Modes

File size V (bit) = frequency  (Hz) * depth i (bit) * time t (sec) * R mode (mono = 1, stereo = 2) V =  * i * t * R

File size V (bits) =
frequency Hz) *
depth i (bits) *
time t (sec) *
R mode (mono = 1, stereo = 2)
V= *i*t*R

Task 1

Task 2

Estimate the information volume of high-quality
1 minute stereo audio file
if the "depth" of coding is 16 bits, and the frequency
48 kHz sampling.
Informational
volume
duration of 1 second is:
sound
file
16 bits 48,000 2 = 1,536,000 bits = 187.5 KB
Informational
volume
duration of 1 minute is equal to:
sound
187.5 KB/s 60 s 11 MB
file