Flashcards in IT152_Lecture_10_Sound_2013a1 Deck (143):
The element of sound can be important to achieve....?
the goals of multimedia Web site.
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.
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...?
- 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 have a recurring pattern; an analogue wave pattern called a...?
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...?
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...?
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 8000 Hz cannot record frequencies above 8000 Hz. In fact, the sound cannot even have frequencies above 4000 Hz. According to the sampling theorem (Nyquist theorem), the maximum frequency is limited to half the sampling rate.
Lambada = ...?
Gamma = ...?
Digitizing or Sound Sampling...?
The process of converting analogue soundto numbers.
An analogue sound that has been converted to numbers.
Two factors that determine sound quality are...?
sample rate and resoultion.
- 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
- 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...?
You can work out the background noise of a digital signal from the...?
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...?
The logarithmic measurement called decibel (dB), is used to...?
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.
flat and unrealistic compared to 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.
downloaded or streamed.
Downloaded audio file must be...?
entirely saved to the user's computer before it can be played.
more advanced process that allows sound file to be played as it is downloading; before entire file is transferred to the user’s computer.
Technique that mathematically reduces size of a file
Beneficial for storing and transferring sound files
Type of Compression applied impacts...?
quality of sound file and file size.
Clip audio gives access to...?
prerecorded digital audio clips of music and sound effects.
Be sure to carefully read the licensing agreements that come with clip audio
In addition to using prerecorded audio files, you can...?
record, digitize, and process your own sound files.
proper planning is critical if sound is to be...?
Preparing digital audio files...?
Digitise the analogue material by recording it onto computer readable digital media.
I.e. play the sound from one device straight into your computer using audio digitising software
Balancing sound quality with available RAM and hard disk resources
Setting proper recording level to get a good, clean recording
File Size v Quality...?
Sampling rate determines frequency makeup
Resolution determines the accuracy with which a sound can be digitised. More bits, more accuracy.
Stereo versus Mono
Humans have 2 ears. Stereo recordings are more lifelike and realistic
Mono recordings sound flat and uninteresting by comparison but are ok for voice narration
Stereo requires twice as much storage space
Minimally, a sound card and software program are needed to...?
The sound card samples or digitizs the sound based on the...?
sample rate (11, 22, or 44 kHz)
(number of bits used to represent each sample such as 8-, 16-, or 24 bit), and then produces the digital approximation of the analog signal.
The 22.05 KHz bandwidth of a compact disc should be enough to reproduce all the ....?
frequencies you can hear.
DAT has a standard sample rate of...?
New standards are evovling that for DVD will give produces the choice of.../
16, 20, 24-bit at either 48KHz or 96KHz
Calculating Audio file sizes....?
- Sampling rate * duration of recording in seconds * (bit resolution/8) * 2 for stereo
- 10 second stereo at 44.1 KHz 16-bit
- 44100 * 10 * 16/8 *2
= 1,764,000 bytes
- 10 seconds mono at 22.05 KHz 8-bit
- 22050 * 10 * 8/8/ *1
= 220,500 bytes
CD-quality stereo recording requires 10.5 Mbytes per minute. (about 74 minutes for a CD)
The number of bits determines how accurately the...?
amplitude of a sample is recorded.
The two most common are 8 bit and 16 bit formats. In an 8 bit sample, there are 256 different levels of amplitude. 16 bit samples have 65,536 levels.
The number of bits is becoming less important due to...?
the variety of audio compression techniques available today, such as RealAudio and MPEG. By using MPEG compression, for example, you can make a sound file anywhere from 10 to 100 times smaller and still maintain excellent quality. In compressed audio, the term "bits" has no meaning in the classical sense.
analog signals into electrical impluses.
An analog-to-digital convert (ADC), converts the electrical implus to...?
numbers that can be stored, understood, and manipulated by a microprocessor.
Too much level will...?
Not enough level and you may get...?
excess residual noise
With digital meters do not let them...?
Every time you cross the 0 threshold you introduce...?
Removing extraneous noises, cutting and pasting shorter pieces.
Splicing and assembly...?
removing extraneous noises, cutting and pasting shorter pieces.
different segments may have differing levels.
your authoring software may read different formats than that captured.
Resampling or downsampling...?
record at 16-bit but downsampled for the project to save disk space.
Fade-ins and Fade-outs...?
Smooth out the very beginning and the very end of a sound file.
modify the recording's frequency content to sound brighter or darker.
alter the length of a sound file without changing the pitch can degrade the audio quality.
Digital Signal Processing (DSP)...?
effects such as reverberation. add depth and dimension.
can produce surreal effects.
Standard format agreed on by the major manufacturers of musical instruments.
MIDI standard was established so...?
musical instruments can communicate sound information with one another.
Music recordings today utilize MIDI as a key enabling technology for recording music. In addition, MID has been adopted into..?
mobile phones, used to play back ringtones.
MIDI was developed in the...?
early 1980's for electronic musical instruments and computers.
MIDI is a protocol that allows....?
detailed descriptions of a musical score, such as notes, sequences of notes, and what instruments will play the notes.
MIDI is NOT...?
digitized sound. It is a shorthand representation stored in numeric form.
Midi file is a list of...?
time-stamped commands that are recordings of musical actions.
The quality of the midi sounds will depend on...?
the quality of the musical instruments and the capabilities of your sound system.
A midi file tends to be...?
significantly smaller than the equivalent digitized waveform file.
Digital audio data is the actual representation of a sound, store in the form of...?
thousands of individual numbers called samples.
The digital data represents the...?
instantaneous amplitude of around at discrete slices of time.
MIDI is not device dependent and...?
sounds the same every time it is played.
The consistency of MIDI pays the price of...?
large data storage requirements.
MIDI data are ...?
Advantages of MIDI...?
- files are much more compact: 200 to 1000 times smaller than CD-quality digital audio files
- may sound better than digital audio if the MIDI sound source is high quality
- files can have the length changed without altering the pitch or degrading the quality. Can manipulate the smallest details of a composition
Disadvantages of MIDI...?
- Playback will only be accurate if the playback device is identical to the device used for production. The sound of MIDI instruments varies according to the playback device and the sound generation method it uses.
- Cannot easily be used to play back spoken dialogue.
- Digital audio has consistent playback quality
A wider selection of application software and system support for digital audio is available
- Do not need a knowledge of music theory to prepare and programme digital audio
Recording, to communicate, MIDI instruments have...?
"in" and "out" ports that enable them to be connected to another MIDI-ready device.
Use MIDI if...?
- Digital audio won’t work through lack of RAM, hard disk space, or CPU processing power
- You have a high-quality MIDI sound source
- You have complete control over the playback hardware
- You do not need spoken dialogue
Use digital audio if...?
- You do not have control over the playback hardware
- You have the computing resources to handles digital files
- You need spoken dialogue
Society of Motion Picture and Television Engineers (SMPTE) was developed to....?
provide frame-accurate video and audio data.
By using professional SMPTE codes, beats of music can be set to...?
match changes in video for all standard video frame rates
To play sound on a computer system, the user needs a ...?
sound card and speakers, or a headset.
The digital audio file is set through a...?
digital-to-analog converter (DAC) so that it can be heard.
Important to test sounds under a variety of...?
Traditional sound studio equipment is...?
utilized to record, mix, edit audio; costs tens of thousands of dollars
With sound editing and mixing software, sound files can be...?
produced for much less money.
Digital audio systems can reproduce the...?
blade and scissors experience of audio tape editing.
Leading digital audio editor for Macintosh platform; ideal formanipulating sound files
Leading developer and marketer of digital media and Internet software tools
Similar to Peak, but designed for Windows platform
Frame-by-frame audio and video synchronization; high-quality streaming media, multitrack recording
music production software offers sound professionals freedom to create custom music
Digidesign Pro Tools...?
world’s leading nonlinear audio editing workstation and solutions
most powerful and popular high-end audio solution on the market
formerly Cool Edit; digital audio software package that is comprehensive, yet easy to learn
All three media players (QuickTime, RealPlayer, Windows Media Player) are...?
- Equipped to open and display most popular audio file formats
- Possess the ability to play live streaming audio
QuickTime and RealPlayer...?
best choices for streaming media. Quick Time to play AAC.
uncompressed formats, such as...?
WAV, AIFF, and AU.
Formats with lossless compression, such as...?
FLAC, WavPack, Shorten, TTA, lossless Windows Media Audio (WMA). FLAC is supported by a wide variety of portable audio playback devices.
formats with lossy compression...?
such as MP3, Vorbis (filename extension OGG), lossy Windows Media Audio (WMA) and AAC.
sound file formats include...?
- AAC (Advanced Audio Coding): AAC is an Audio Codec* see notes page
- also used by Apple 's iTunes and Dolby Digital, also known as AC-3.
- format of choice for Web as encoding more efficient than MP3 and better quality
- AAC is used in movie theatres for surround sound systems that carry more than two channels.
audio codec is a computer program that..?
compresses/decompresses digital audio data according to a given audio file format or streaming audio format
MIDI (Musical Instrument Digital Interface)...?
Internationally accepted file format for storing MIDI data. Very small and efficient. Not actual music but instructions to play music.
MP3 (MPEG—Audio Layer 3)...?
- Open standard technology uses the MPEG-1 audio layer 3 codec to provide acceptable lossy compression for music files of up to to 14:1
- The compression is about 10:1 compared with uncompressed WAV files therefore a CD with MP3 files can store about 11 hours of music, compared to 74 minutes
- Most common audio format on the Web
MPEG Audio strips information that is not important. Based on the...?
research of human perception and the encoder decides what information is elementary and what can be stripped.
Before we can hear anything, the incoming data is analyzed by our...?
(RA, RAM, RM): Excellent compression, incredibly popular, widespread support for streaming audio. Requires plug-in.
compressed Macromedia Flash or Shockwave Flash file type designed for animation
is an unpatented, free codec.
- Waveform format; Commonly used, supported format on Windows
- Usually quite big