Storing Sound Data

Posted: March 19, 2012 in Uncategorized

RAW: This file type uses pulse code modulation. This method encodes information in a signal by varying the amplitude of the pulses. This limits pulse amplitude to several predifined values.

RIFF: This file type uses ADPCM(Adaptive Pulse Code Modulation). This method compresses data that has been encoded in the PCM form. It stores only the changes between the samples, not the sample themselves. This compresses PCM data by a ratio of 4:1 since it uses only 4 bits for the sample change rather than the 16 bits for the original PCM value.

MP3: This file type uses lossy compression that does not seriously degrade the quality of the sound it filters out.

Revision Post

Posted: January 9, 2012 in Uncategorized

In total I have done about 7 hours or so of revision. I studied only the topics I felt most weak in. This is a brief summary:

Computer Structure

CU: The Control Unit (CU) sends out control signals:

  • Within the processor to move data from one register to another and to activate specific ALU functions;
  • To the control bus to read to or write from memory;
  • To I/O modules

Data bus: The lines on the data bus enable data to be transferred between system modules. The width of the data bus is measured by the number of lines on the data bus. Each line can carry one bit at a time and the width is important in determining how well a system performs.

Address bus: This holds the address of the memory location being accessed. The more lines on the address bus, the more locations the system can address. The maximum number of addresses = 2^width of the address bus.

Interrupt Line: A signal on the interrupt line causes the current routine being carried out to be suspended and gives control of the processor to another routine, for example, one inputting data from a mouse or keyboard.

The Fetch – Execute Signal: This describes how the processor fetches instructions from memory then carries them out. It divides neatly into two parts:

Fetch: this part of the cycle reads the next instruction from main memory into the processor;

  • The memory address of the next instruction is placed on the address bus;
  • A read signal is activated on the read lines;
  • The data stored at the addressed memory location is placed on the data bus and transferred to a register which holds it until it is executed (carried out).

Execute: this part interprets and performs the instruction;

  • The Processor interprets the instruction;
  • The Processor carries out the instruction.

MIPS: MIPS is short for millions of instructions per second. This approach to gauging the system performance is based on the measurement of the number of machine code instructions that are processed in a second. This type of measurer doesn’t take into account the size and complexity of the instructions being carried out and so is generally seen as giving you a rough indication.

FLOPS: FLOPS is short for floating point operations per second. This measures how many floating operations the processor can carry out in a second. This type of measurer is generally seen as a more reliable indicator than MIPS. This is because it is an objective approach measuring the number of clearly definable, arithmetical tasks that can be carried out in a second.

Voltage conversion: Peripherals mainly work at higher voltage levels than the CPU. These signals need to be reduced to the CPU’s level and this is one of the jobs of the interface. For example, a signal coming from a keyboard at 9V needs to be reduced to level which can be handled by the CPU, a maximum of 5V.

Protocol Conversion: Peripherals send data in units of varying sizes and at speeds that are different from those that operate in CPU. The interface has to deal with the differences between them.

Also the software development section was revised aswell.

In this section input devices will be considered : an overview of each device, a technical summary and capacity, speed and accuracy of each device.

Keyboard:

A keyboard in computing terms is the equivelent to a typewriter. It uses an arrangement of buttons to act as mechanical levers. The most common type of keyboard in todays day in age is a QWERTY keyboard.

In using a Keyboard the type of data transmission is serial. This is were the digital data is sent one bit at a time. This shows that as each key is pushed the data is sent to the interface individually.

A keyboard has no capacity in which no data is stored inside the keyboard as it has no memory.

Mouse:

A mouse in computing terms is basically a device used to navigate your way around the screen. It uses either a rollerball or laser device to allowing movement on the screen. A typical type of mouse is this Logitech mouse shown.

The mouse, as always, drives the clock line for the serial data transmission. The mouse is now initialized.

Scanner:

A scanner is basically a photographic device used to capture an image, whether that be from a magazine or book. Bit Depth varies depending on the scanning array characteristics, but is usually at least 24 bits. High quality models have 48 bits or more bit depth. Another qualifying parameter for a scanner is its resolution, measured in pixels per inch (ppi). This determines the quality of the image scanned using OCR(Optical Character Recognition).

Microphone:

A microphone is a device used to convert sound into an electrical signal. Many microphones are used for musical purposes, but are also used for communication such as Skype etc.

Sampling in microphones consists of taking samples per second from a continuous, discrete signal. A common measure for sampling is HZ which is frequency. Compression is a process that reduces the dynamic range of an audio signal, that is, narrows the difference between high and low audio levels or volumes.

Digital Video Camera:

A digital video camera is used for filming. It functions by using 24 frames per second. This then uses the images taken every 25th of a second to make a video.

Output Devices

InkJet Printer:

An InkJet printer is a type of computer printer which creates a digital image by propelling droplets of ink onto the paper. Printer Spooling is when your computer temporarily stores data for the printer to use later. It basically speeds up system performance due tot the fact it stores extra pages until they needed to be printed. The printer has a capacity allowing it to store data. This comes in handy when multiple pages are being printed as a method called spooling. This is a technique is used in the transfer of data to a slow peripheral, in this case a printer.

Lazer Printer:

A laser printer is a type of computer printer that quickly produces high quality text and graphics on paper. This printer has a capacity and it uses a method called buffering which allows the data to be sent to the buffer which hence allows the CPU to go of to do other jobs. The speed of one of printers is much faster than an innkjet and produces more pages per minute. Heres a image of how a lazer printer works:

CRT Monitor:

This is a monitor that has a vacuum tube containing an electron gun which fires phosphor paint onto the screen to display an image. It has no capacity meaning no data is stored in the monitor. Inside a CRT display unit, a triad is a group of three colored red, green, and blue, which enable the color display by use of directing differing intensities of the electron beams. A triad enables display a color by combining the red, green and blue elements. Each triad results in one pixel of the displayed image. In a CRT, the raster is a sequence of horizontal lines that are scanned rapidly with an electron beam all over the screen, similar to a TV. The diffrences though are that the resolution is usually better. The refresh rate  is the number of times in a second that display hardware draws the data. This is distinct from the measure of frame rate in that the refresh rate includes the repeated drawing of identical frames, while frame rate measures how often a video source can feed an entire frame of new data to a display.

Aside  —  Posted: December 12, 2011 in Uncategorized

Addressability

Posted: December 5, 2011 in Uncategorized

Computer memory is divided up into memory locations. Each location has its own unique address. The processor uses this address to find the data and instructions it needs. The number of memory locations that a processor can address is, in theory, limited by the number of lines in the address bus.

Memory

Posted: December 5, 2011 in Uncategorized

This section will look at the types of main memory and cache along with their uses:

Random Access Memory: Random Access Memory is very volatile. The data that is held in RAM is lost when the system is shut down. RAM also holds the computer’s programs and data while they are being processed.


DRAM: And no before you say it, it is not a measure of whisky! This stands for Dynamic RAM which is almost identical to RAM but in this case it must refresh its contents otherwise they are deleted.

SRAM: Static RAM doesn’t need to be refreshed as long as there is power applied to the system. For example this could be used to store dates etc when the computer has no mains supply.

Cache: This is Memory that is located very close to the CPU which is often used to store instructions and speed up system performance.

ROM: Read Only Memory is permanent memory. All data remains situated on the chip even when the power is switched off. Is commonly used for storing programs fixed on during the manufacturing stage. It is also used to store the Bootstrap Loader which is used to load the OS.

Virtual Memory: This uses Hard Disk space temporarily as a storage area. This is much slower than using RAM.

Bitmapped Graphics

Posted: November 4, 2011 in Uncategorized

In digital imaging, a pixel, picture element is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled.

Resolution is the number of bits that is whithin a fixed area, e.g usually cm/2

Black and white images are represented through using binary i.e 0 or 1 per pixel.

100000001 = 2 black pixels and 7 white pixels

Colour images are represeneted through many colours for each pixel. For instance four colours can be represented in 2 bits.

Bit depth is the number of bits used to represent the colours of the pixels.

Binary

Posted: November 3, 2011 in Uncategorized

Binary is the main numeric system used in computers. They use binary instead of decimal methods, as there are simply less rules to follow. Binary is a series of electrical voltages/pulses holding either the value 0 for off and 1 for on. To convert binary to decimal we take each bit as a value:

The number 53 can be represented as : 00110101 (128,64,32,16,8,4,2,1)

The binary number 11100011 = 227

For more than 8 bits we simply take 2^number of bits, for the largest number represented and 2^n-1 for the range.

Negative Numbers

These are the inverse of positive numbers. To represent these in binary form we do the following:

Take 53 = 00110101 / We Inverse all the numbers so…..

11001010 + 1 = 11001011 = -53/ This technique is called Bits two complement!