Kavya

Speed of Sound

The speed of sound is a term used to describe the speed of sound waves passing through an elastic medium.

The speed varies with the medium employed (for example, sound waves move faster through water than through air), as well as with the properties of the medium, especially temperature.

Sound travels slower in lower temperature and faster in higher temperature.

Speed of Sound at Different Mediums:

MEDIUM	SPEED (m/s)
Air	343
Helium	962
Water	1500
Steel	5600

Sound is propagation of local disturbance in a medium.

Molecules in a solid are more tightly packed than those in gases.

So it is easier for solid molecules to collide with neighboring molecules and facilitate the propagation of disturbance.

How to measure sound travel in air:

The average speed of sound through air is about 1130 feet per second (344 meters per second) at room temperature. However, changes in temperature and humidity will affect this speed.
Here is a simple way to measure the speed at which sound travels through air. You'll need the following items:

Two blocks of wood, or other items that make a loud, sharp sound when struck together.
A stopwatch
A friend to help with the experiment
A tape measure

Instructions:

Find a large empty area, such as a field or large court.
Choose two spots on opposite ends of the area where each person will stand.
Measure the distance between the two spots using a tape measure. Alternatively, you can count off measured steps between the two spots.
Have your friend take the blocks and stand at one spot, holding them up high.
Take the stopwatch and stand at the other spot. Make sure you have a clear view of the blocks.
Signal your friend to bang the two blocks together hard.
Start the stopwatch as soon as you see the blocks hit each other.
Press stop as soon as you hear the sound from the blocks.
Calculate the speed of the sound by dividing the distance between you and your friend by the elapsed time. To get a more accurate measurement, repeat the above steps a few times and then take an average of the results.

Other Examples of Measuring the Speed of Sound:

Measuring of Speed of Sound Using Microphone

MP3 Compression

Mp3 are audio files compressed using lossy compression.

The lossy compression allows great savings in file size, with the average MP3 file being 90% smaller than an equivalent uncompressed audio file.

Like all lossy compressed files, savings in size are made by deleting data that the computer believes is redundant and will not be missed by the user.

MP3 audio compression reduces a file size through:

Perceptual music shaping
Reducing the audio bitrate

Perceptual Music Shaping:

Perceptual music shaping refers to the process of removing inaudible sounds in order to make a file size smaller.

Inaudible sounds may include noises at frequencies that human cannot hear, quiet sounds that cannot be heard over louder sounds.

Bitrate:

In audio files, the bitrate is the number of bits that need to be processed every second. This is measured in kilobits per second.

The bitrate is calculated by multiplying the sample rate by the bit depth and number of audio channels.

The bigger the bitrate, the better the sound quality, but the larger the file size.

Sample Rate:

The sample rate (measured in Hz or kHz) is the number of samples (snapshots in time) of sound that are recorded to represent an audio performance.

Taking more samples per second will result in a more accurate and better sounding audio file. However, increasing the sample rate increases the file size.

Bit Depth:

Bit depth is the number of bits of information recorded in each sample.

MP3 with a high bit depth will contain a wider spectrum of frequencies, giving a more accurate recording of the audio performance. However, the higher the bit depth, the greater the file size.

Advantages:

The low data size (file size) is the biggest advantage. A smaller file size enables the user to rip a large amount of music files on a disc.

The files can be easily shared via an online medium (Internet) or a physical medium (USB, CDs).

Time taken to download and upload files has reduced significantly. MP3s can be downloaded through HTTP or FTP sites. Earlier if a single music file download would take hours, with this technology the time is reduced to only a few minutes!

MP3 files can be played by many types of devices such as CD players and Apple iPods. You can also play MP3 files with media players such as Winamp, Windows Media Player, or QuickTime.

Disadvantage:

The biggest disadvantage is the low audio quality. MP3 uses a "lossy" algorithm that deletes the "lesser audible" music content in order to reduce the file size, thus compromising on the music quality.

CAT and MRI Scans

CAT Scan:

The term CAT stnads for "Computerized Axial Tomography" also called as CT Scan.

It refers to a computerized X-ray imaging procedure in which a narrow beam of X-rays is aimed at a patient and quickly rotated around the body, producing signals that are processed by the machine’s computer to generate cross-sectional images or slices of the body.

These slices are called tomographic images and contain more detailed information than conventional X-rays.

Once a number of successive slices are collected by the machine’s computer, they can be digitally “stacked” together to form a three-dimensional image of the patient that allows for easier identification and location of basic structures as well as possible tumors or abnormalities.

Unlike a conventional x-ray which uses a fixed X-ray tube, a CT scanner uses a motorized X-ray source that rotates around the circular opening of a donut-shaped structure called a gantry.

During a CT scan, the patient lies on a bed that slowly moves through the gantry while the X-ray tube rotates around the patient, shooting narrow beams of X-rays through the body.

Instead of film, CT scanners use special digital x-ray detectors, which are located directly opposite the X-ray source. As the X-rays leave the patient, they are picked up by the detectors and transmitted to a computer.

Each time the X-ray source completes one full rotation, the CT computer uses sophisticated mathematical techniques to construct a 2D image slice of the patient.

When a full slice is completed, the image is stored and the motorized bed is moved forward incrementally into the gantry.

The X-ray scanning process is then repeated to produce another image slice. This process continues until the desired number of slices is collected.

Image slices can either be displayed individually or stacked together by the computer to generate a 3D image of the patient that shows the skeleton, organs, and tissues as well as any abnormalities the physician is trying to identify.

This method makes easier to find the exact place where a problem may be located and this method is also used to identify disease or injury within various regions of the body.

MRI Scan:

Magnetic resonance imaging (MRI) is a type of scan that uses strong magnetic fields and radio waves to produce detailed images of the inside of the body.

An MRI scanner is a large tube that contains powerful magnets. You lie inside the tube during the scan.

Most of the human body is made up of water molecules, which consist of hydrogen and oxygen atoms.

At the center of each hydrogen atom is an even smaller particle, called a proton.. Protons are like tiny magnets and are very sensitive to magnetic fields.

Most of the human body is made up of water molecules, which consist of hydrogen and oxygen atoms. At the center of each hydrogen atom is an even smaller particle, called a proton. Protons are like tiny magnets and are very sensitive to magnetic fields.

Short bursts of radio waves are then sent to certain areas of the body, knocking the protons out of alignment. When the radio waves are turned off, the protons realign and this sends out radio signals, which are picked up by receivers.

These signals provide information about the exact location of the protons in the body. They also help to distinguish between the various types of tissue in the body, because the protons in different types of tissue realign at different speeds and produce distinct signals.

In the same way that millions of pixels on a computer screen can create complex pictures, the signals from the millions of protons in the body are combined to create a detailed image of the inside of the body.

CAT vs MRI Scan:

Unlike CAT Scans, which use X-rays, MRI Scans use powerful magnetic fields and radio frequency pulses to produce detailed pictures of organs, soft tissues, bone and other internal body structures. Differences between normal and abnormal tissue is often clearer on an MRI image than a CT.
CAT Scan is good for seeing organs and bone details whereas MRI Scan is good for seeing soft tissue.
MRI Scan takes longer time (30mins or more) than the CAT Scan (5-10mins)

CAT Scan vs MRI Scan

Radar Systems

RADAR stands for Radio Detection and Ranging System.

It is basically an electromagnetic system used to detect the location and distance of an object from the point where the RADAR is placed.

It works by radiating energy into space and monitoring the echo or reflected signal from the objects. It operates in the UHF and microwave range.

The RADAR system generally consists of a transmitter which produces an electromagnetic signal which is radiated into space by an antenna.

When this signal strikes any object, it gets reflected or reradiated in many directions.

This reflected or echo signal is received by the radar antenna which delivers it to the receiver, where it is processed to determine the geographical statistics of the object.

Types of Radar:

There are basically three types of Radars

1.Continuous Wave Radar (CW Radar):

A block diagram of simple CW radar is shown in below figure.

The transmitter generates a continuous (unmodulated) oscillation of frequency F0, which is radiated by the antenna.

A portion of the radiated energy is intercepted by the target and is scattered, some of it in the direction of the radar, where it is collected by the receiving antenna.

If the target is in motion with a velocity Vr relative to the radar, the received signal will be shifted in frequency from the transmitted frequency F0 by an amount ±Fd .

The plus sign associated with the doppler frequency applies if the distance between target and radar is decreasing (closing target), that is, when the received signal frequency is greater than the transmitted signal frequency.

The minus sign applies if the distance is increasing (receding target).

The received echo signal at a frequency F0 ± Fd enters the radar via the antenna and is heterodyned in the detector (mixer) with a portion of the transmitter signal/o to produce a doppler beat note of frequency Fd. The sign Fd is lost in this process.

2.Pulse Radar:

Pulse radar that extracts the Doppler frequency-shifted echo signal.

A simple way to convert the CW radar to the pulse radar by turning on and off CW oscillator to generate pulses.

This way of generation of pulses removes the reference signal, which is required to recognize the Doppler shifts.

One way to introduce the reference signal is shown in below figure. Here the power amplifier is turned on and off to generate the high power pulses.

The received echo signal is mixed with the output of CW oscillator, which acts as coherent reference to allow the recognition of any change in the frequency.

Here coherent means that the transmitted pulses are synchronously used as reference signal. The change in frequency is detected through Doppler filter.

3.Moving Target Radar (MTI Radar):

The doppler frequency shift produced by a moving target may be used in a pulse radar. just as in the CW radar, to determine the relative velocity of a target or to separate desired moving targets from undesired stationary objects (clutter).

Such a pulse radar that utilizes the doppler frequency shift as a means for discriminating moving from fixed targets is called an MTI (moving target indication) or a pulse doppler radar.

The block diagram of MTI Radar system is shown below, the significant difference between this MTI configuration is the manner in which the reference signal is generated.

The coherent reference is supplied by an oscillator called the coho, which stands for coherent oscillator.

The coho is a stable oscillator whose frequency is the same as the intermediate frequency used in the receiver. In addition to providing the reference signal. the output of the coho. fc is also mixed with the local-oscillator frequency fl.

The local oscillator must also be a stable oscillator and is called stalo, for stable local oscillator.

The stalo, coho, and the mixer in which they are combined plus any low-level amplification are called the receiver-exciter because of the dual role they serve in both the receiver and the transmitter.

The characteristic feature of coherent MTI radar is that the transmitted signal must be coherent (in phase) with the reference signal in the receiver.

The reference signal from the coho and the I F echo signal are both fed into a mixer called the phase detector. The phase detector differs from the normal amplitude detector since its output is proportional to the phase difference between the two input signals.

Applications of Radar Systems:

Used in Military for Target Detection, Target Tracking and Weapon Control

Used in Air Traffic Control

Used to Avoid Collisions in Ships

Used in Submarines

Digital Synthesizer

A synthesizer is an electronic keyboard that can generate or copy virtually any kind of sound, making it able to mimic the sound of a traditional instrument, such as a violin or piano, or create brand new, undreamed of sounds like the crunch of footsteps on the surface of Mars or the noise blood cells make when they tumble through our veins.

"Synthesize" means to make something new, often by putting it together from existing pieces. So we can think of a synthesizer as an electronic gadget that makes new sounds by piecing together "old" ones.

What makes one instrument sound different from another?

When two instruments play exactly the same musical note, at roughly the same volume, they can sound completely different.

If we play a pure musical note with a tuning fork, the oscilloscope shows an undulating hilly pattern called a sine wave.

But if we play the same note with a trumpet, the wave will look more zig-zagged, like the teeth of a saw (it's usually called a saw-tooth wave).

If we play the same note again on a flute, we will see triangular waves, while a clarinet, blown hard, playing exactly the same note, might well give us square waves.

The shape of the sound waves , which is controlled by how the instrument pumps energy into the world around it.

In other words, how it vibrates and makes the air around or inside it vibrate in sympathy is one of the things that makes instruments sound different from one another.

You can hear the difference between sine waves, square waves, and sawtooth waves in this little sound clip. In each case, we're hearing a note with exactly the same frequency (440 Hz):

How Synthesizer Works?

Generate sound waves of different shapes.

Generate more than one sound tone at once to produce a fundamental frequency and harmonics.

Make the volume of the sound change over time to produce different ADSR envelope shapes.

Examples:
1.Basic Harmonics:

In my first attempt at synthesizing a sound, I've added together three square waves of 110 Hz (top), 220 Hz (middle), and 440 Hz (bottom).

Then I've faded in the sound at the start (giving a slowly rising attack) and faded it out at the end (giving an even more gradual release), so there's no decay or sustain.

That gives me these three fish-shaped envelopes, which are added together in the final sound, the three tones play simultaneously, but our ears add them together so we hear a single, fused sound about 0.5 seconds long.

The result sounds fairly harsh not something I'd particularly want to listen to

2.Adding a wah-wah effect:

Next, I've taken the same three waves and applied a wah-wah effect, which wobbles the amplitude up and down to resemble a human voice.

Notice how this changes the envelopes of the waveforms without changing the frequencies of the sounds.

The higher frequency sounds are changed more than the lower frequency sound.

It sounds much less abrasive and a bit more interesting. With more work, we could get this quite close to a human vowel sound.

3.Adding Noise:

For my final example, I've reduced the amplitude of the middle tone by about 50 percent.

Removed the lowest tone entirely, and replaced it with white noise that attacks and decays in roughly the same time period.

Here's what it sounds like more windy and whistle-like, but still recognizably the same note (frequency).

Digital Communication

Digital Communication is a mode of communication where the information or the thought is encoded digitally as discrete signals and electronically transferred to the recipients.

Digital Communication is one of the most commonly used modes of communication now a days.

Basic Elements of Digital Communication System:

Information Source and Input Transducer: The source of information can be analog or digital, e.g. analog such as audio or video signal, digital such as teletype signal.
Source Encoder: The signal produced by source is converted into digital signal consists of 1's and 0's.The process of efficiently converting the output of analog or digital source into a sequence of binary digits is known as source encoding.
Channel Encoder: The purpose of the channel encoder is to introduced, in controlled manner, some redundancy in the binary information sequence that can be used at the receiver to overcome the effects of noise and interference encountered in the transmission on the signal through the channel.
Digital Modulator: The binary sequence is passed to digital modulator which in turns convert the sequence into electrical signals so that we can transmit them on channel.
Channel: The communication channel is the physical medium that is used for transmitting signals from transmitter to receiver.
Digital Demodulator: The digital demodulator processes the channel corrupted transmitted waveform and reduces the waveform to the sequence of numbers that represents estimates of the transmitted data symbols.
Channel Decoder: This sequence of numbers then passed through the channel decoder which attempts to reconstruct the original information sequence from the knowledge of the code used by the channel encoder and the redundancy contained in the received data.
Source Decoder: Source decoder tries to decode the sequence from the knowledge of encoding algorithm. And which results in the approximate replica of the input at the transmitter end.
Output Transducer: Finally we get the desired signal format analog or digital.

Applications:

Speech Processing
Speech Recognition
Digital Image Processing
Audio Signal Processing

Speech Recognition

Speech Recognition, the ability of devices to respond to spoken commands.

It enables the recognition and translation of spoken language into text.

Voice recognition systems enable consumers to interact with technology simply by speaking to it, enabling hands-free requests, reminders and other simple tasks.

How Voice Recognition Works?

Voice recognition software on computers requires that analog audio be converted into digital signals, known as analog-to-digital conversion.

For a computer to decipher a signal, it must have a digital database, or vocabulary, of words or syllables, as well as a speedy means for comparing this data to signals.

The speech patterns are stored on the hard drive and loaded into memory when the program is run.

A comparator checks these stored patterns against the output of the A/D converter and this action is called pattern recognition.

Uses of Voice Recognition Technique:

You can also use speech recognition software in homes and business.

A range of software products allows users to dictate to their computer and have their words converted to text in a word processing or e-mail document.

You can access function commands, such as opening files and accessing menus, with voice instructions.

Some programs are for specific business settings, such as medical or legal transcription.

Real Time Applications of Speech Recognition Technique:

Google Mini Home and Amazon Alexa Used to control Home Appliances

Used in Robotics

Voice Operated Cars