Objectives: to acquaint with sound information and its characteristics; teach to process sound information on a computer.

Requirements for knowledge and skills

Students should know:

What is audio information;

What is loudness, tone, intensity, frequency;

The concepts of "sampling rate", "audio coding depth";

Sound processing software and hardware.

Students should be able to:

Digitize audio information;

Edit the entry;

Apply sound effects;

Save audio files in various formats.

Software and didactic equipment: Ugr., § 1.5, p. 40; demonstration "Encoding audio information"; projector; sound editor Audacity.

DURING THE CLASSES

I. Organizational moment

II. Knowledge update

What types of perception information do you know? (Visual, auditory, kinesthetic, smell, taste.)

What type of information does a person perceive in the greatest amount? (Visual.)

III. Setting lesson goals

The second largest volume of perceived information is sound.

And what is it? (A wave that travels through air, water, or other medium.)

IV. Work on the topic of the lesson

(Explanation is accompanied by the demo "Encoding Audio Information".)

A sound wave propagates in any environment with continuously varying intensity and frequency, with varying volume and tone.

What is the name of the unit for measuring loudness? (Decibel.) A change in sound volume by 10 dB corresponds to a change in sound intensity by a factor of 10.

In order for a computer to process sound, it must be digitized. This is done using time sampling. The sound wave is broken into temporary pieces, for each of which its own value of sound intensity is set.

What hardware is needed to work with audio information? (Microphone, sound card, speaker.)

Sound quality depends on the sound sampling rate - the number of sound volume measurements in one second. This value takes values \u200b\u200bfrom 8000 to 48000. Each piece of a sound wave has its own sound volume level, which requires a certain amount of information to be encoded - the sound coding depth. During the encoding process, each volume level is assigned its own 16-bit code.

Which digitized sound will be the lowest quality and which will be the highest? (Telephone communication, ayduo-CD.)

The higher the sound quality, the larger the audio file.

- What software is needed to work with sound? (Player, sound editor.)

Sound editors allow you to record, play, and edit sound (delete, copy, move parts of the audio track, overlay each other, apply acoustic effects, change the sampling rate and coding depth).

There are three groups of audio file formats:

Uncompressed audio formats such as WAV, AIFF;

Lossless compression audio formats (APE, FLAC);

Lossy audio formats (shr3, ogg).

V. Practical work

See the full content of the lesson at the link below:

Practical work 1.5

Audio coding and processing

Hardware and software. A computer with a Windows operating system installed, a sound card, a connected microphone, and speakers (or headphones); sound editor Audacity 2.0.

Objective. Learn to digitize sound, edit sound recordings and save sound files in various formats.

The task.Record digitized audio, edit the recording, overdub two recordings, apply sound effects and save audio files in various formats.

Encoding and processing of audio information in the Audacity sound editor

Launch the Audacity sound editor with the command [ Start - All Programs -Audacity – Audacity].

Let's set the audio sampling rate to 22050 Hz and the audio coding depth to 16 bits.

In the application window, execute the command [ Edit - Options]. In the dialog box that appears, select the item Quality... In the corresponding fields in the drop-down lists, select the sampling frequency and audio coding depth (audio bit depth):

Press OK.

Let's record the digitized sound.

To stop recording, click on the button Stop .

A graphical display of the dependence of the volume of the recorded digitized sound on time will appear in the application window.

Let's get acquainted with the points of digitization, displayed on the graph of the dependence of the sound volume on time.

In the application window, enter the command [ View - Zoom in]. The time scale will be significantly stretched, and the sound sampling points will become visible on the graph:

Let's edit the digitized sound: transfer the initial fragment of the recording to its end.

Position the cursor at the end of the recording and press the button Paste or execute the command [ Edit - Paste].

Listen to the edited recording by clicking on the button on the toolbar Play .

Let's mix (overlay) two records.

Open the second audio file audio. mp3 stored on the local disk using the command [ File - Import - Sound file ...]. The required sound file is located along the path: My documents - Grade 9 - Blanks.

Listen to the overlay of two recordings by first placing a vertical mark (cursor) at the beginning of the audio tracks by clicking the mouse or pressing a key Home, and then clicking on the button on the toolbar Play.

Let's apply various sound effects to the recording ( Fade in, Speed \u200b\u200bchange, Pitch change, Echo other).

Select the second record or its part with the mouse and sequentially execute the commands [ Effects - Fade in ...], [Effects - Pitch bend ...], [Effects - Change of speed ...], [Effects - Echo ...] other.

After each application of effects, listen to the resulting sound processing results.

Let's save the digitized and processed sound in a sound file

To save the processed sound in the native format of the Audacity program, execute the command [ File - Save Project As ...]. In field File name: enter file name - Sound... Save the project in its own folder.

To save a sound file in the universal WAV format, execute the command [ File - Export ...]. In the dialog box that opens, enter the file name ("Sound") and specify the file type (WAV) and the save path (own folder).

In the window that appears Editing metadata in the corresponding text fields, you can enter data that will be saved in the properties of the sound file.

Press the button OK.

To save an audio file in MP3 format, repeat step 10 (in the drop-down list Ty n file:select - FilesMP3 ). Save the file in its own folder and under the same name.

Compare the information volumes of audio files saved in different formats.

... for them, and for most adults, this is terra incognita, they need a guide to this world, the world of unexpected effects, the world of discoveries, which for the majority remains unknown ... CoolEdit program - allows you to see what you hear, and to see exactly what as discussed in this lesson. All these are the results of the ADC operation. Using its capabilities, you can create a lot of different lessons. For example, how do you like the topic: “Mom's record is a chipped edge, about love for us, about love for us, play something ...”, or “Moving sound in space,” or “Sound detective,” etc.

Lesson: Encoding and Processing Sound Information

Lesson objectives:

Developmental and educational goals	Means of Achievement	Control technology
Get the skills to handle sound files.	Work in the program CoolEdit96, Processing of sound files.	Visual control and listening
Develop the skill of using the keyboard and mouse when performing cut, copy and paste operations.	Operations with files and their fragments.	Visual.
Awaken a sense of responsibility when dealing with local nature.	Demonstration of illustrations, playback of sound files. Work on editing the file.
Increase the vocabulary of not only Russian, but also English words	Using the English version of the program for processing sound files.	Pronunciation of words in English.
To develop the ability to navigate the computer file system when searching for files.	Search for the desired sound file.	Controlling the student's speed.
Learning objectives	Means of Achievement	Control technology
Get to know the technology of binary encoding of Wav files	Demonstration of illustrations and posters, methods of working with files. Issuance of reference notes.	Solving problems
Learn to solve problems to determine the volume of a sound file in WAV format	Demonstration of an algorithm for solving such problems.	Solving problems
Learn to open, edit, process and save sound files	Practical work on the task file.	Assessment of the implementation of practical work.

Lesson provision:

A tape recorder, multimedia computers, speakers and headphones, a program for processing sound files Cool Edit 96, sound files with sounds of animals and birds, posters, pictures of animals and birds, pictures of the forest, cards with tasks, instruction cards for working with the program Cool Edit 96 . (Multimedia projector and presentation can replace tape recorder and posters.)

Lesson plan

	Teacher actions	Student actions	Time (min)
	Inclusion in the lesson.	Listen. Write down the topic.
	Explains the principles of audio coding.	Draw a basic outline.
	Describes an algorithm for solving problems.	Solve problems.
	Set a goal for practical work - processing a sound file of the WAV format. Checks the solution of problems. Helps those who find it difficult in practical work.	Take up space for a PC. Using ready-made reference notes for working with the COOL EDIT 96 program, open and process the audio file. Save the editing results. Determine the size of the file
	Pronounces the closing word. Gives those who have completed the work photographs of animals found in the area, the sounds of which the students heard. Conducts eye exercises.	Do eye exercises
	Summarizes the lesson, announces grades and homework.	Write down homework

A detailed outline of one of the lesson options

Lesson start

Mute scene and sign showing: hello, sit down. Open your notebooks. Write down the topic of the lesson. Sound coding and processing.

Probably at the beginning of our lesson you were missing audio information. The ability to use and process sound has long attracted computer and software developers. I will ask you to give me other types of information before starting work on a new topic. (Sound, graphic, text, numeric, video.)

Right! And in what form is it stored inside the computer? (Discrete, binary.)

And where can it be stored? (RAM, Winchester, Floppy disk)

What information will be discussed today in the lesson? (Sound.) As we have already remembered, all information in the PC is presented in discrete, binary form. Sound is no exception.

But what is sound? (Air vibrations.) CONTINUOUS signal. (Analog, as it is called.) How is it converted?

Demonstration

(A presentation or poster is used.) First, the sound is converted to an electrical signal using a microphone. To convert a continuous audio signal (vukorecording) into numerical form, a special device is used that is part of the sound card - it is called an ADC (analog-to-digital converter). It is this device that measures the electrical signal at very small, regular intervals, converts the measurement result into a binary number and transfers it to the PC's RAM.

The signal is measured with limited accuracy. And for storing each measured value, a multi-bit memory cell is allocated.

What should be the sampling rate if we want to describe the original signal very accurately?

(If we want to get an exact copy of the signal, then the sampling rate must be large (high), higher than the frequency of the encoded sound). For CD recording quality, this frequency should be 44100 Hz (once per second).

The quality of the recording is also affected by the bit width of the binary number, which describes one signal value. It is taken equal to 4, 8, or 16 bits.

We calculate the volume and sounding time of audio files

One of the tasks of computer science is to be able to calculate the amount of information. Tell me, what files volume have you already counted? (Graphic files) The task of finding the amount of information contained in a sound file is practically no different from the previous one, and now we will try to calculate the amount of information contained in a sound file in WAV format.

There are pieces of paper on your tables, please sign them and read the work algorithm - on the back.

So, we read the algorithm: Algorithm 1 (Calculate the information volume of a sound file):

1) find out how many values \u200b\u200bare read into memory during the sound of the file;

2) find out the bit depth of the code (how many bits in memory each measured value occupies);

3) multiply the results;

4) convert the result to bytes;

5) convert the result to K bytes;

6) translate the result into M bytes;

We read the algorithm: Algorithm 2 (Calculate the playing time of the file.)

1) Transfer the information volume of the file into K bytes.

2) Transfer the information volume of the file into bytes.

3) Convert the information volume of the file into bits.

4) Find out how many values \u200b\u200bwere measured in total (Information volume in bits divided by the length of the code).

5) Calculate the number of seconds of sound. (Divide the previous result by the sample rate.)

Time is given for an independent decision

Algorithm and theory will come in handy when preparing for the computer science exam. At home, glue them into your notebooks. Hand over the leaflets with the solved problems, after checking they will return to you.

And I ask for a moment of attention.

Epigraph to practical work

Every living being is beautiful. Beauty is hidden in his existence and in his proximity to nature, his adaptability to it. Its beauty also lies in the fact that no creature will kill another just for the sake of its own whim, and not for food for the sake of ...

And people ... sometimes forget about it. And picking up guns, they fire left and right, becoming enemies to nature and to themselves. Because of such a hunt, some species of animals completely disappear on our land ... forever. I suggest that you take the first step towards rectifying this situation. At least in the imagination.

You have a SOUNDS folder in your computers, your task files, and I suggest you edit them by deleting the sounds of shots and insert the sound of the camera shutter instead.

The key to completing the task is on your desk.

Get started!

Practical work, checking tasks.

The practical work is described for the student in the instruction card located on the table at the computer; the names of the files with sounds can be written in advance on the same instruction card.

Epilogue and eye exercises

Look behind the monitors and pick up photos. These are the animals and birds of our region. Some of them are already threatened with extinction. These are the animals that you saved and whose sounds you heard.

And look at the photo of the forest for a few seconds, relax, sit comfortably, close your eyes. Imagine how good it is for animals and birds in your house when no one bothers them ... Do not open your eyes ... look up. Try to see the tops of trees and a clear sky, Lower your eyes, lower them, and imagine a clear river in which a fish is splashing, Now turn your eyes to the left and to the right, flowers and berries around you can be heard singing of birds and buzzing insects ... (at this stage of the lesson you can turn on PC files with stereo sound and ask students to turn their eyes towards certain sounds with their eyes closed)

Now open your eyes. Everything on our Earth can disappear just as what was in your imagination disappeared. Be more careful with nature, because no digitized sound can replace live sound for us, and nothing can replace the beauty of living nature for us.

(On that note, we conclude our lesson by announcing grades and homework.)

Of course, today we could not use all the features of the program, if you wish, you can copy it and try to master it at home yourself. It fits on one floppy disk.

Attachment 1

Basic outline for the student

All information in the PC is presented in discrete, binary form. Sound is no exception. The ability to process audio has long attracted computer and software developers.

First, the sound is converted into an electrical signal using a microphone. To convert a continuous audio signal (sound recording) into numerical form, a special device is used that is part of the sound card - it is called an ADC (analog - digital converter). It is this device, at very small, regular intervals, that measures the electrical signal, converts the measurement result into a positive or negative binary number and transfers it to the PC's RAM.

The frequency at which the signal is measured is called the sampling rate.

For a high recording quality (CD recording quality) this frequency should be 44 100 Hz (once per second), i.e. twice the frequency of the highest sound that a person can hear.

To encode each measured value, a four-, eight-, or sixteen-bit code is used, depending on the desired recording quality. (With 16-bit coding, the value of the amplitude of the audio signal is most accurately described, which means its quality is higher)

The reverse conversion from binary codes to an analog electrical audio signal is performed using a DAC - digital-to-analog converter, also included in the sound card

Tasks

One of the tasks of computer science is to be able to calculate the amount of information contained in a sound file. You may come across 2 types of audio coding tasks. In some, by the known playing time, it will be necessary to find out the information volume of the file, in others, by the known file size, to find the time of its sound.

Problem 1

____________________

Hint algorithms

Algorithm 1(Calculate information volume of audio file)

Find out how the values \u200b\u200bare read into memory during the sound of the file;

Find out the bit depth of the code (how many bits in memory each measured value occupies);

Multiply the results;

Convert the result to bytes;

Convert the result to Kbytes;

Convert result to MB.

Algorithm 2(Calculate the playing time of the file.)

Convert the information volume of the file into Kbytes.

Convert the information volume of the file into bytes.

Convert the information volume of the file into bits.

Find out how many values \u200b\u200bwere measured in total. (Divide the bits by the length of the code.)

Calculate the number of seconds of sound. (Divide the previous result by the sample rate.)

Appendix 2

Instructions card for working in the program Cool Edit 96.

1) Launching the program from the working folder - Fig. 5

2) mark the indicated radio buttons and press ABOUTFig. 7

3) Select in the program menu one by one the items File, Open ..., set the type of files to open ALL (*. *) (see figure) and Open a WAV file specified by the instructor.

4) Listen to (PLAY) and view the file. Determine the location in the shot file that you want to delete.

5) Using the operations of selection "with the mouse", select and delete a fragment of the sound file. (Edit, Delete)

6) Add the camera shutter sound to your file. (File, Open Append ..., Select a file named Shutter.wav)

7) Listen to the file again. (PLAY)

8) Review the file parameters in the CoolEdit96 program window. Will your file fit on a floppy disk?

As you can see, editing audio files is not that difficult. Show and let the teacher listen to your work, he is worried about you, because you are doing this for the first time.

Additional task

View your file at maximum magnification (Press Zoom multiple times)

Did you see the results of measurements made by the ADC?

Try to increase the signal amplitude by dragging with the “mouse” the markers at the measurement points

Reset the magnification and listen to the file with the “click” sound you created.

You can try to fix the file defect.

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Annotation to the presentation

The presentation was created to help the teacher conduct a computer science lesson. A detailed and accessible presentation of the main questions will allow schoolchildren, if necessary, to get acquainted with the school section of ICT on their home computer. The content of the show helps in the development of students' ability to think abstractly, compare and analyze.

1. Sound information
2. Timing audio sampling
3. Quality of digitized audio
4. Sound editors

Format

pptx (powerpoint)

Number of slides

The audience

The words

Abstract

Present

Purpose

• Presentation made by student for grade

Slide 1

Slide 2

Sound information

• A person perceives sound waves in the form of sound of varying volume and tone.
• The higher the intensity of the sound wave, the louder the sound, the higher the frequency of the wave, the higher the tone of the sound.
• Low sound
• Alt
• volume

Slide 3

• The human ear perceives sound with a frequency of 20 (low sound) to 20,000 (high sound) vibrations per second.
• A special unit "decibel" is used to measure the loudness of sound.

Slide 4

Digitization (digitizing)

• 1011010110101010011
• analog signal
• digital signal
• analog signal

Slide 5

Timing audio sampling

• In order for the PC to be able to process sound, the continuous audio signal must be converted into digital discrete form using time sampling (the continuous wave is divided into separate small sections, the value of the sound intensity is set for each such section)
• On the graph, it looks like this:
• A, the volume
• t, time

Slide 6

• Time sampling

Slide 7

• The audio sampling rate is the number of measurements of the volume of a sound in one second.
• The audio sampling rate can range from 8000 to 48000 changes in audio volume per second.

Slide 8

• Audio coding depth is the amount of information required to encode the discrete loudness levels of digital audio.
• If the coding depth is known, then the number of digital sound volume levels can be calculated by the formula
• N- number of sound volume levels
• I- coding depth
• N \u003d 2I

Slide 9

Quality of digitized audio

• Depends on:
• sampling rate;
• sampling depth.
• The higher the frequency and sampling depth of the sound, the better the sound of the digitized sound will be.
• The higher the digital sound quality, the larger the information volume of the audio file.

Slide 10

Sound editors

Sound editors allow you to not only record and play sound, but also edit it. They allow you to change the sound quality and volume of the audio file.
The digitized audio can be saved uncompressed in the universal wav format or in the mp3 compressed format.

• WAV (Waveform audio format), often uncompressed (size!)
• MP3 (MPEG-1 Audio Layer 3, lossy compression)
• WMA (Windows Media Audio, streaming audio, compression)

Slide 11

• An example of solving the problem:
• Let's estimate the volume of a stereo sound file with a duration of 1 second with an average sound quality (16 bits, 24000 measurements per second).
• V \u003d 16 * 24000 * 2 (since stereo - 2 tracks) \u003d 768000 bits \u003d
• 96000 bytes \u003d 94 KB

View all slides

Abstract

The purpose of the lesson:

Lesson type: Reiteration

Equipment:

During the classes:

Organizing time

Statement of the educational problem:

Brainstorm

Captains competition

Show yourself

Collective creativity

Wall to wall

Summarizing

Attachment 1

Input device

Output device

Memory

Notation

Logics

Coding

Appendix 2

Appendix 3

Sample questions:

Give a definition to the concept "Input device". Give examples of such devices.

Give a definition of the concept "Output device". Give examples of such devices.

Give a definition to the concept of "Computer memory". Give examples of such devices.

Give a definition to the concept of "Number system". Give examples of systems you are familiar with. Remind about the alphabet of each system.

Give a definition to the concept of "Logic". Give examples of logic elements (Draw a table of values)

Give a definition to the concept of "Coding". Tell me how to encode with ASCII code table

Convert number 001101 to decimal notation

Convert Binary number 572

Convert 011001 to decimal notation

Convert Binary number 525

Convert 010101 to decimal notation

Convert Binary number 521

Used Books:

_1368534147.unknown

_1368534144.unknown

Lesson plan on the topic: "Repetition of the material covered in a year"

The purpose of the lesson: Review the material learned over the year and consolidate the most difficult topics.

Lesson type: Reiteration

Equipment: Computers, handouts (Code tables), multimedia projector, whiteboard, textbooks, notebooks, pens.

During the classes:

Organizing time

Statement of the educational problem:

The analysis of the tests showed the topics that caused the greatest difficulties.

Today in the lesson we will fix the most difficult moments and repeat some of the editors. I suggest breaking up into groups and holding competitions. For each complete answer, the team receives 2 points, for an incomplete answer or a significant addition to the opponent's answer 1 point. (divided into 3 groups and commanders are selected)

Brainstorm. (repetition of system unit devices). Speed \u200b\u200bcommand responses on presentation slides.

Captains competition... Repetition of theoretical material

Team captains pull 2 \u200b\u200bquestions. The team helps prepare the answer to the question. The captain answers. (Attachment 1). This appendix contains sample questions with answers. You can take questions that need to be repeated.

Show yourself... Application of theoretical knowledge in practice.

Each team must draw a picture in a graphics editor and type the text according to the proposed sample (pre-prepared cards are handed out) For this, 2 people from the team are invited. As long as your team members complete the proposed task, all other team members continue to earn points. You were given the task of coming up with messages to your rivals. I suggest to encode it using the ASCII code table. Exchange messages. The opposing team must decode the message received. These tasks will take 10 minutes to complete.

Collective creativity... Solving problems, signs are distributed into it, you can enter a task according to logic (Appendix 2 and 3)

Wall to wall... The teams take turns asking questions prepared in advance. If the opposing team cannot answer the question, answer the question asked yourself.

Summarizing... Scoring. Lesson discussion.

Attachment 1

Give a definition to the concept "Input device". Give examples of such devices.

Input device Are hardware for converting information from a human-readable form to a computer-readable form.

Give a definition of the concept "Output device". Give examples of such devices.

Output device Is hardware for converting a computer representation of information into a form that a person can understand.

Give a definition to the concept of "Computer memory". Give examples of such devices.

Memory Is a collection of devices for storing information.

Give a definition to the concept of "Number system". Give examples of systems you are familiar with. Remind about the alphabet of each system.

Notation Is a set of techniques and rules for writing numbers using a specific set of characters

Give a definition to the concept of "Logic". Give examples of logic elements (Draw a table of values)

LogicsIs the science of the laws and forms of thinking (conjunction, disjunction, negation, consequence and equivalence)

Give a definition to the concept of "Coding". Tell me how to encode with ASCII code table

Coding Is the process of representing data as code.

Appendix 2

You can offer any example, and distribute a sign as a card

Appendix 3

Convert number 001101 to decimal notation

Convert Binary number 572

Convert 011001 to decimal notation

Convert Binary number 525

Convert 010101 to decimal notation

Convert Binary number 521

Sample questions:

Give a definition to the concept "Input device". Give examples of such devices.

Give a definition of the concept "Output device". Give examples of such devices.

Give a definition to the concept of "Computer memory". Give examples of such devices.

Give a definition to the concept of "Number system". Give examples of systems you are familiar with. Remind about the alphabet of each system.

Give a definition to the concept of "Logic". Give examples of logic elements (Draw a table of values)

Give a definition to the concept of "Coding". Tell me how to encode with ASCII code table

Convert number 001101 to decimal notation

Convert Binary number 572

Convert 011001 to decimal notation

Convert Binary number 525

Convert 010101 to decimal notation

Convert Binary number 521

Used Books:

S.V. Simonovich "General Informatics"

S.V. Simonovich "Practical Informatics"

N.V. Makarov "Informatics" grade 7-9

Points are awarded as stars

_1368534147.unknown

_1368534144.unknown

Download abstract

The human ear perceives sound at a frequency of 20 vibrations per second (low sound) to 20,000 vibrations per second (high sound).

A person can perceive sound in a huge range of intensities, in which the maximum intensity is 10 14 times greater than the minimum (one hundred thousand billion times). A special unit is used to measure sound volume "decibel" (dbl) (Table 5.1). Decrease or increase in sound volume by 10 dB corresponds to a decrease or increase in sound intensity by 10 times.

Time sampling of sound. In order for a computer to process sound, a continuous audio signal must be converted to digital discrete form using time sampling. A continuous sound wave is broken into separate small time sections, for each such section a certain value of sound intensity is set.

Thus, the continuous dependence of the sound loudness on time A (t) is replaced by a discrete sequence of loudness levels. On the graph, this looks like replacing a smooth curve with a sequence of "steps" (Fig. 1.2).

Figure: 1.2. Timing audio sampling

Sampling frequency. A microphone connected to the sound card is used to record analog sound and convert it to digital form. The quality of the obtained digital sound depends on the number of measurements of the sound volume level per unit of time, i.e. sampling rate... The more measurements are made in I second (the higher the sampling rate), the more accurately the "ladder" of the digital audio signal repeats the dialog signal curve.

Audio sampling rate is the number of sound volume measurements in one second.

The audio sampling rate can range from 8000 to 48000 sound volume measurements per second.

Audio coding depth. Each "step" is assigned a specific value for the sound volume level. Sound loudness levels can be considered as a set of possible states N, for coding of which a certain amount of information I is required, which is called the audio coding depth.

Audio coding depth is the amount of information required to encode the discrete loudness levels of digital audio.

If the coding depth is known, then the number of digital sound loudness levels can be calculated using the formula N \u003d 2 I. Let the sound coding depth be 16 bits, then the number of sound volume levels is:

N \u003d 2 I \u003d 2 16 \u003d 65 536.

During the encoding process, each sound volume level is assigned its own 16-bit binary code, the smallest sound level will correspond to the code 0000000000000000, and the highest - 1111111111111111.

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

It should be remembered that the higher the digital sound quality, the larger the information volume of the audio file. It is possible to estimate the information volume of a digital stereo sound file with a duration of 1 second with an average sound quality (16 bits, 24,000 measurements per second). To do this, the coding depth must be multiplied by the number of measurements in 1 second and multiplied by 2 (stereo sound):

16 bits × 24,000 × 2 \u003d 768,000 bits \u003d 96,000 bytes \u003d 93.75 KB.

Sound editors. Sound editors allow you to not only record and play sound, but also edit it. The digitized sound is presented in sound editors in a visual form, so the operations of copying, moving and deleting parts of the audio track can be easily performed using the mouse. In addition, you can superimpose audio tracks on top of each other (mix sounds) and apply various acoustic effects (echo, playback in reverse, etc.).

Sound editors allow you to change the digital sound quality and volume of an audio file by changing the sampling rate and encoding depth. Digitized audio can be saved uncompressed in audio files in a universal format Wav or in compressed format MP3.

When storing audio in compressed formats, audio frequencies with low intensity "excessive" for human perception are discarded, coinciding in time with audio frequencies with high intensity. 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).

Control questions

1. How does sampling rate and coding depth affect digital audio quality?

Self-help assignments

1.22. Selective answer assignment. The sound card performs binary encoding of the analog audio signal. How much information is needed to encode each of the 65,536 possible signal strength levels?
1) 16 bits; 2) 256 bits; 3) 1 bit; 4) 8 bits.

1.23. A task with a detailed answer. Estimate the information volume of digital audio files with a duration of 10 seconds at a coding depth and sampling rate of an audio signal that provide the minimum and maximum sound quality:
a) mono, 8 bits, 8000 measurements per second;
b) stereo, 16 bits, 48,000 measurements per second.

1.24. A task with a detailed answer. Determine the length of a sound file that will fit on a 3.5 "floppy disk (note that 2847 sectors of 512 bytes each are allocated to store data on such a floppy disk):
a) with low sound quality: mono, 8 bits, 8000 measurements per second;
b) with high sound quality: stereo, 16 bits, 48,000 measurements per second.