Learning Resources
Lesson
Convergence is the act of moving together or finding a common form. Media convergence has been occurring over several years as all forms of media become digital (created in a digital format and distributed in a digital format). While the medium of delivery still is identifiable as magazines, movies, TV, radio, newspapers and so on, the media (content) is entirely digital and can be moved easily from one delivery medium to another. Some tweaking of materials may be required. Colours, for example, have different characteristics when produced by a TV screen, computer monitor, or ink on paper and must be modified according to where it will be physically produced. But the creation of the media or content is almost entirely done in a digital workspace. This is a quite recent development and is still in evolution.
Analogue, Analog, and Digital
Analogue
An analogue is something that is similar to, or representative of, something else. It is a likeness that permits one to draw an analogy (Miriam-Webster Dictionary). An analogy is a comparison of two or more things that in some way reference the same idea, or represent different ideas in parallel ways.
Historically, people created images, carvings, sculptures, paintings and literature as analogues of important cultural, historical and personal events and ideas. Typically, a person from that culture could examine the media and understand what it represented. They could infer meaning from the shape, texture, colour, or arrangement of the components of the media. Meaning came from the form of the media, from the way information and ideas were encoded. The media was an analogue of the real event. Line and texture in a painting can be visually processed by our eyes and brain as representative of the real. The way information is encoded is what evokes meaning. The flow of words in verse and prose can stir emotions, both in what it says directly and in what we infer from the content as being analogous to a similar personal experience.
Media, then can be an analogue of real life and is used to store the collective ideas and experiences of a culture, as well as to create dialog.
Analog
An analog is a representation of information by encoding data in a continuously variable physical form. A clock with moving hands is analog. Music recorded on vinyl platters (LPs) is analog. Music recorded on cassette tape is analog. VHS and 8mm video tape record information in analog format. While paintings and sculpture and books encode media in analog form, we are more concerned with technologies that are designed to encode media in less obvious, but still analog, forms. For example
- LPs (which have been mostly displaced by CDs) store music in a spiral groove in the surface of a vinyl disc.
The groove has bumps in the sides, corresponding to the music. As the disc spins, a needle following the groove moves up and down and left to right with the bumps. The up-down motion is converted to a corresponding continuously variable electrical voltage through electromagnetic means. Similarly, the left-right motion is converted to a corresponding continuously variable electrical voltage. The two electrical signals provide two channels of audio information, referred to as stereo. When the signals are amplified and sent to speakers, they produce the audio (more or less) as it was originally recorded.
- Audio and video tape store audio and video as continuously variable magnetic patterns on the surface of an acetate, polyester, or mylar tape. A blank tape has a uniform coating of magnetic particles. To encode information, the tape passes over an electromagnetic recording head. The continuously changing electrical signal creates a corresponding variable magnetic field in the recording head. As the tape passes over the head, the pattern is written into the magnetic coating. Playback is the reverse. As the tape passes over the playback head, the continuously changing magnetic pattern induces a similarly patterned electrical voltage in the playback head. The electrical signal is interpreted by the rest of the device and presented as sound and video images.
Until very recently, all radio, TV, and most audio and video recording used analog encoding. The information was encoded as continuously variable electrical signals, and stored as magnetic patterns which are analogues of the electrical signal. Different analog media use different technologies to encode, store, retrieve and transmit the data. Transferring data from one analog media to another is very difficult.
Digital
Digital is the representation of information in numerical digits. Most often, information is encoded using only two digits - 0 and 1 - called bits. Digital information is made up of discrete bits of information. This is fundamentally different from analog data, which is continuously variable.
Since the world inhabited by humans is primarily analog (continuously variable), it is frequently necessary to convert information from analog to digital, and from digital back to analog. These two processes are called analog-to-digital conversion, and digital-to-analog conversion.
A-D, and D-A Conversion
Analog-to-digital conversion
Analog-to-digital conversion involves a process called sampling. At set time intervals, the strength of the analog signal is measured, and that measurement is converted to a binary number. Analog-to-digital encoding is done with an ADC (Analog-Digital Converter). Essentially, and ADC converts a signal having many possible states to one having only two possible states.
Several things determine the fidelity (how well the reproduction matches the original) of the resulting digital encoding of the analog signal
- Frequency of sampling, also called the sampling rate.
- Resolution of the sample, also called sampling precision
The sequence of images below illustrates this concept. The first image illustrates an analog signal. The next 2 show a low sample rate and low resolution samples. The last 2 show a higher sample rate, and higher sampling precision. Note the difference in effect when the reproduced curve is drawn alongside the original analog signal.
Figure Analog Signal
An analog signal is a continuously variable voltage over time. Time is shown measured in milliseconds.
Figure Digital Samples taken every 10 milliseconds
Note that the resolution is 0.2 volts, and the sampling rate is 1 sample per 10 milliseconds or 100 samples per second (1000 milliseconds in a second).
Figure Reproduced Signal
When the signal is reproduced through digital-to-analog conversion, there is a big difference between the original line and the reproduced line. The error was caused by the low sampling rate and low resolution. This difference is called the sampling error. Music sampled at this rate and precision would not sound very close to the original.
In order to improve the accuracy, it is necessary to increase the sampling rate and the precision at which each sample is measured. The next sequence illustrates a smaller sampling error.
Figure Increased Sampling Rate and Sampling Resolution
Figure Improved Reproduced Signal
Notice how closely the reproduced line matches the original line. The Sampling error is greatly reduced.
Music CDs are typically encoded with data taken with a sampling rate of 44,000 samples per second (44KHz). Sampling precision is measured in steps called bits. The examples showed volts as the unit of measure. While it is the voltage that is being measured, the actual measurement is given in bits. An 8-bit measurement allows 28 or 256 steps. A 12-bit measurement allows 212 or 4096 steps, which is a significant increase in precision. A 16-bit measurement allows 216 or 65,536 steps. This is a major increase in precision.
Figure Sample Precision
As the figure illustrates,
- if you use a sample precision of 8 bits, a signal of 2 volts will be measured in 2/256 or .00781 volt increments
- if you use a sample precision of 12 bits, a signal of 2 volts will be measured in 2/4096 or .000049 volt increments
- if you use a sample precision of 16 bits, a signal of 2 volts will be measured in 2/64,536 or 0.00003 volt increments
The smaller the voltage change that can be measured, the higher the fidelity the digital record will have with the original analog signal.
Putting all that together, the following sequence shows the conversion from an analog to a digital signal
Figure Samples with 12 bit precision (4096 steps)
Figure Samples Converted to Binary Digits
The analog signal, represented by the curved line is converted to a string of 0's and 1's. Since it is 12 bit precision, the numbers are in groups of 12 0's and 1's with one group for every sample taken.
If you do the math, a single channel audio file using 12bit precision and a 44KHz sampling rate with 40 minutes of music has
12 bit times 44000 samples/sec times 60 sec/min times 40 minutes
or 1.5 bytes X 44000 X 60 X 40 = 158,840.000 bytes
Digital-to-analog conversion
Digital encoding is a means of creating an extremely accurate record of an analog signal. It can be stored, used, and copied as often as you wish, with absolutely no loss in quality. This is completely different than the methods used to record analog signals, all of which lose quality over time, with use, and with copying.
In many instances, there is no need to convert the digital signal back to analog. Sometimes it is necessary. The conversion process is called digital-to-analog conversion. Digital-to-analog conversion is done with a DAC (Digital-analog Converter). A DAC converts a signal from one having only two possible states to one having many possible states. It is the reverse of analog-to-digital conversion.
The sequence below illustrates the process
Figure The Signal in Binary Format
Figure the Binary Signal Converted to 12 Bit Steps (12 bit precision)
Figure The Re-created Analog Signal as 12 bit Steps
Figure The Re-created Analog Signal as a Continuously Variable Voltage
As you can see, the fidelity the recreated analog signal from the digital-to-analog conversion process is entirely dependant on the frequency of sampling and the sample precision used in the analog-to-digital conversion process.
Summary
All media is an analogue of ideas and experiences. The creator/viewer/user/consumer of the media creates and interprets it according to cultural and personal experiences.
Analog is a means of encoding data in a continuously variable physical form. It is independent of how one interprets meaning. The encoded data can be understood by humans as representative of the thing being encoded (for example if the voltage pattern of an audio recording is examined, one can readily see the shape of the audio).
Digital is a means of encoding data in zeros and ones. It is also independent of how one interprets meaning. The encoded data cannot be directly understood by humans as representative of the thing being encoded (for example, if the data encoded for an audio recording is examined, one can see no relationship between the zeros and ones and the audio)
Activity
Assigned Activities
Please complete the following
- Compile a list of media formats from the past 30 years which have been recorded and/or transmitted (used, viewed, listened to, read, ...) in analog format
- Compile a list of media formats which are recorded and/or transmitted in digital format
- Create an entry in your course portfolio for the information you have compiled
- Publish the entry to your course portfolio web
Test Yourself
There is no self test for this lesson.