IT152_Lecture_10_Sound_2013a1 Flashcards
The element of sound can be important to achieve….?
the goals of multimedia Web site.
Sounds add…?
another dimension.
If improperly created, sound files can…?
take too much time to download.
Providing controls (such as skip, pause, mute, volume adjustment, etc.) is an…?
effective way of keeping users involved and movitivated.
Sound is produced by the….?
vibration of an object in air or water. THe vibration creates waves of pressure. The vibrations of vocal cords or guitar strings produce sound waves.
Sound waves are characterised by…?
their speed, or frequency, and their amplitude.
Acoustics is the science of sound. The decibel measurement is a ratio between a…?
reference point on an logarithmic scale and the level that is experienced.
Streaming audio…?
the sound file will begin playing after part of the file is downloaded.
The decision to incorporate sound into a multimedia Web site should be consistent with…?
the goals of the multimedia Web site.
Web sites designed for entertainment have background music that sets….?
the mood to light and cheery, or dark and dreary.
Audio can either be synched with the occurrence of other objects in the production, or it can…?
serve as a trigger when clicked.
Sounds are either…?
content sounds or ambient sounds.
Content sounds furnish…?
information.
- Narration, dialogue are content sounds.
Ambient sounds reinforce…?
messages and set the mood.
Many splash screens or intro pages use…?
background music to set a mood.
When you speak, vibrations, called ____ ____, are created.
sound waves
Sound waves have a recurring pattern; an analogue wave pattern called a…?
waveform.
Sound is produced by the vibration of an object in air or water. The vibration creates waves of pressure. The vibrations of vocal cords or guitar strings produce sound waves. These waves travel at a speed determined by…?
the air temperature and density. At 20C in dry air at sea level it is 768 miles per hour, 1236 km/hr or 343 m/sec, known as Mach 1. The speed of sound changes for different substatnces and in liquids and non-porous solids it is faster than in air. (Water it is 1,484 m/s which is 4.3 times faster than air).
Amplitude refers to the …?
percieved loudness of sound. The amplitude is measured in decibels. Distance between the valley and the peak of a waveform.
Decibel (dB) smallest variation in…?
amplitude detected by the human ear.
- 70dB voice ~ 100dB car on motorway ~ 160dB Turbo-jet engine.
Frequency is releated to the…?
number of times the sound wave completes a cycle in one secon measured in hertz (Hz). Our ears detect frequency as pitch or tones. Themore cycles per sec, the higher the pitch. Humans have a range of approx from 20 Hz to 20 KHz
- Number of peakes that occur in one ec measured by the distance between the peaks.
Amplitude determines volume which is measured in…?
decibels.
Frequency determine…?
the pitch - the greater the distance between the peaks, the lower the sound.
Sound is energy, like waves on a beach, too much amplitude (noise level) and you can…?
damage your ears.
The perception of loudness is dependent on…?
frequency.
At low frequencies more power is needed to deliver…?
the same level of percieved loudness as for a sound at middle or higher frequencies.
Age plays a part as well…?
A five year old will hear a 1KHz tone played at 20dB while an older adult will not.
A tenfold increase in output power results in a…?
10 dB increase.
The perceived loudness doubles for every…?
6 dB increase.
Some noise comparisons…?
30dB Very soft whisper 70 dB Voice conversation 90 dB Shouting Voice 100 dB Car on a motorway 120 dB Jack Hammer 160 dB Turbo-jet engine at take-off 195 dB Saturn Rocket
Average human hearing spans a frequency range from about…?
20Hz to about 17000 Hz (20Hz max).
The frequency range of a digital sound is limited by …?
its sampling rate. In other words, a sound sampled at 8000Hz cannot record frequencies above 8000Hz. In fact, the sound cannot even have frequencies above 4000Hz. According to the sampling theorem (Nyquist theorem), the maximum frequency is limited to half the sampling rate.
Lambada = …?
wavelength.
Gamma = …?
amplitude.
Digitizing or Sound Sampling…?
The process of converting analogue soundto numbers.
Digital Audio…?
An analogue sound that has been converted to numbers.
Two factors that determine sound quality are…?
sample rate and resoultion.
Sample rate…?
- Number of waveform samples per second or the number of times the sample is taken.
- The amount of information stored about each sample is the sample size. The more often you sample the more data you store but the finer the resolution and quality of the captured sound.
- Measured in kilohertz, with 11 kHz, 22 kHz, and 44 kHz being the most common sampling rates
Resoultion…?
- Number of binary bits processed for each sound wave
- Sometimes referred to as sample size
- As the number of bits used to sample the sound increases, the range and the quality of the sound also improves
CD’s have a bit depth of…?
16 bits. (This means that the sound can, in theory, be digitised with a precision of 16 bits or 65536 levels of equal units to describe the dynamic range.)
A 8-bit sample provides…?
256 equal units to describe the level of sound at the time the slice of sound is captured
The value of each sample is rounded off to the…?
nearest integer (quantization). If the amplitude is greater than the intervals available, clipping of the top and bottom of the wave occurs.
16-bit shound shuld allow you to hear the sound without…?
errors.
You can work out the background noise of a digital signal from the…?
bit depth.
The maximum error between the real sound and …?
the digitised version is half the minimum step in digitisation.
Since 16 bit has 65536 steps and 8 bits has only 255 steps you can see that the 8 bit sound will be 256 times as…?
noisy as a 16 bit sound.
Our ears do not respond to sound in a…?
linear fashion.
The logarithmic measurement called decibel (dB), is used to…?
measure sound.
This means we do not actually hear 256 times more noise in an 8 bit recording. The signal to noise ration of a 16-bit system is 98dB (which basically means you wont hear anything) whereas for an 8-bit system it is 50dB.
every 6 dB increment makes a sound…/
twice as loud, this means that 8 bit is eight times as noisy as 16 bit. Also note that noise only occurs in the sound, not in the silences. It will be very noticeable on slight noises like rustles, so these should be removed from the recording destined for 8 bit.
If there are frequencies higher than the 1/2 the sample rate you will get…?
spurious samples that will sound like squeaking. Beware this when you down-sample. Filter before you do it.
With digital audio recording a balance has to be struck between…?
recording at so high a level that you risk overloading, which means clipping the waveform and distortion, and recording so quietly that noise becomes noticeable. Some professional systems now record at 20 or 24 bits (24 bits means the noise is 150dB down). For distribution the sound is converted back to 16 bit so it can go on a CD.
To convert 16 bit to 8 bit the procedure is to…?
divide each sample value by 256 and round the errors. From 8 to 16 you multiply the sample value by 256. This will cause the errors to be multiplied so a re-graded 16 bit will not sound any better than the orginial 8 bit recording.
Aliasing occurs when…?
the sampling rate is not high enough to correctly capture the shape of the sound wave. The recorded sound will have missing tones or new tones that never existed in the original sound. These problem can be eliminated by using higher sampling rates or by using anti-aliasing filters.
Clipping errors occur when the …?
level is too high to be stored in the bits available. For example, if the maximum level for a 16 bit sample is 32767, and the actual level is 40000, then it must be clipped to 32767 to fit. This generates distortion. To eliminate clipping, adjust the recording volume before recording. By using the Control window’s Monitor input feature, you can adjust the volume to a suitable level. The volume is low enough when the VU Meter visual does not reach the top of the red region.
Mono sounds…?
flat and unrealistic compared to stereo sounds.
Stereo sounds…?
Much more dynamic and lifelike.
Mono sound files are sometimes a more appropriate choice on…?
Web where storage and transfer are major concerns.
