UNDERSTANDING SOUNDSSOUNDS FOR DIGITAL ARTS

WHAT IS SOUND?• PROVIDES THE POTENTIAL OF ENTERTAINING, INFORMING AND

EDUCATING INDIVIDUALS WITH THE DIVERSE APPLICATIONS.

• SOUND REACHES THE EARS AS WAVES OF RAPIDLY VARYING AIR PRESSURE CAUSED BY A VIBRATING OBJECT, SUCH AS A GUITAR STRING.

• AS THE STRING MOVES IN ONE DIRECTION, IT PUSHES NEARBY AIR MOLECULES, CAUSING THEM TO MOVE CLOSER TOGETHER.

• THIS CREATES A SMALL REGION OF HIGH PRESSURE ON ONE SIDE OF THE STRING AND LOW PRESSURE ON THE OPPOSITE SIDE.

• AS THE STRINGS MOVES IN THE OPPOSITE DIRECTION, THE AREAS OF HIGH AND LOW PRESSURE REVERSES.

SOUND WAVES• OCCURS AS THESE REPEATING CYCLES OF HIGH AND LOW

PRESSURE MOVE OUT AND AWAY FROM THE VIBRATING OBJECT.

• THE REPEATED WAVEFORMS CREATE THE SAME SHAPE AT REGULAR INTERVALS.

• AN AREA SHOWS ONE COMPLETE SHAPE CALLED PERIOD

• THIS TYPE OF OCCURANCE WITH A CLEARLY DEFINED PERIOD IS CALLED THE PERIODIC WAVEFORM

• PERIODIC WAVEFORMS INCLUDE THOSE FROM MUSICAL INSTRUMENTS, WHISTLING OF THE WIND, VOWEL SOUNDS AND BIRD SONGS. WHILE SOUND CREATED FROM UNPITCHED PERCUSSIONS, RUSHING WATER, COUGHS, AND SNEEZES PRODUCE NON-PERIODIC WAVEFORMS.

THE TWO ELEMENTS OF SOUND

• AMPLITUDE/INTENSITY• DESCRIBED AS THE HEIGHT OF EACH PEAK IN THE

SOUND WAVE

• THE SOFTNESS AND LOUDNESS OF THE SOUND

• HIGHER AMPLITUDE, LOUDER THE SOUND CREATED

• MEASURED WITH DECIBELS(MEANS ONE TENTH(DECI) OF A BEL (ALEXANDER GRAHAM BELL))

THE TWO ELEMENTS OF SOUND

• FREQUENCY/PITCH• DISTANCE BETWEEN THE PEAKS OF THE WAVEFORMS

• MEASURE IN HERTZ(HZ), OR CYCLES PER SECOND.• THIS IDENTIFIES HOW MANY TIMES THE VIBRATION COMPLETES A

CYCLE IN ONE SECOND

• THE ABBREVIATION, KHZ FOR KILOHERTZ IS USED TO INDICATE THOUSANDS OF CYCLE PER SECOND.

• A HUMAN EAR IS CAPABLE OF HEARING FREQUENCIES FROM 20 TO 20,000 HERTZ

HOW THE COMPUTER REPRESENTS SOUND

• TO BE ABLE TO INCLUDE A SOUND TO A MULTIMEDIA APPLICATION, SOUND WAVES MUST FIRST BE TRANSFERRED TO THE COMPUTER.

• THIS PROCESS REQUIRES THAT THE SOUND WAVES BE FIRST CONVERTED FROM AN ANALOG TO A DIGITAL FORM.

ANALOG AND DIGITAL AUDIO

• ANALOG AUDIO• SOUND IS NATURALLY ANALOG SIGNAL

• IT IS CONTINUOUS, WHICH MEANS THAT THERE ARE NO BREAKS OR INTERRUPTIONS

• ONE MOMENT FLOWS INTO THE NEXT

• THE CHANGES IN PITCH CAN BE EASILY DETECTED WHEN SOUND IS CREATED

ANALOG AND DIGITAL AUDIO

• DIGITAL AUDIO• THIS ARE NOT CONTINUOUS

• THEY USE SPECIFIC VALUES TO REPRESENT INFORMATION

• REPRESENT PITCH AND VOLUME OVER THE LENGTH OF THE RECORDING

• IT IS NO LONGER ANALOGOUS, INSTEAD, THE VALUE OF THE SIGNAL IS SAMPLED AT REGULAR INTERVALS BY AN ANALOG-TO-DIGITAL (A/D) CONVERTER OR (ADC). WHICH PRODUCES NUMBERS THAT REPRESENT THE VALUE OF EACH NUMBER

ADVANTAGES OF DIGITAL AUDIO

• THE FOLLOWING ARE THE ADVANTAGES OF DIGITAL AUDIO• WIDER DYNAMIC RANGE

• EASIER TO COPY/REPRODUCE

• BETTER STORAGE CAPABILITY

• ERROR CORRECTION

• DURABILITY

ANALOG TO DIGITAL CONVERSION

• SOUNDS USE ANALOG SIGNALS

• HUMAN VOICE RECORDED IN A TAPE, OR EVEN WHEN SOMEONE TALKS OVER THE TELEPHONE, THE SOUND CREATED IS CONVERTED INTO ANOTHER FORM OF SIGNAL WHICH IS DIGITAL IN FORM.

• THE SOUNDS ARE CONVERTED USING A CIRCUIT CALLED ADC (ANALOG TO DIGITAL CONVERTER) BEFORE ONE CAN MANIPULATE THE SOUNDS IN A DIGITAL EQUIPMENT.

SAMPLING

• A TERM USED TO REPRESENT THE PROCESS OF CONVERTING ANALOG SOUNDS TO DIGITAL SOUNDS.

• IN THIS PROCESS, THE COMPUTER MEASURES THE AMPLITUDE OF THE WAVEFORM AT REGULAR TIME INTERVALS TO PRODUCE SERIES OF NUMBERS.

• EACH OF THE THESE MEASUREMENTS IS CALLED A SAMPLE, WHILE THE PROCESS ITSELF IS CALLED SAMPLING

• THE SAMPLE CREATED IS EASILY STORED IN THE COMPUTERS MEMORY AND CAN BE REPLAYED AT ANY MOMENTS.

TWO FACTORS AFFECTING THE SAMPLE• SAMPLING RATE• DESCRIBED AS THE NUMBER OF TIMES THE SAMPLE

IS TAKEN

• THE RATES ARE TAKEN AS HERTZ AND KILOHERTZ.

• THE MOST COMMON SAMPLING RATES ARE 11.025, 22/05 AND 44.1 KHZ

• THE HIGHEST FREQUENCY THAT A DIGITALLY SAMPLE SIGNAL CAN REPRESENT IS EQUAL TO HALF THE SAMPLING RATE. THUS 44.1 KHZ CAN ONLY BE 22.05 KHZ. CLOSE TO WHAT THE HUMAN EAR CAN HEAR

TWO FACTORS AFFECTING THE SAMPLE• SAMPLING SIZE• COMMONLY TERMED AS QUANTIZATION

• IS THE AMOUNT OF INFORMATION STORED ABOUT THE SAMPLE

• THIS DEPENDS ON NUMBER OF BITS (BINARY DIGIT) USED IN MEASURING THE HEIGHT OF THE WAVEFORM.

• THE MOST COMMON AUDIO RECORDING SIZES ARE 8, 16 AND 20-BIT DEPTH

• USING ADC, ANALOG AUDIO CAN BE CONVERTED.

• UNCOMPRESSED DIGITAL AUDIO KNOWN AS DIGITAL PULSE CODE CAN BE CONVERTED TO ANALOG FORMAT USING DAC.

FILE SIZE AND BANDWIDTH• DIGITAL AUDIO CAN CREATE LARGE FILES THAT QUICKLY

USE UP HARD DISK CAPACITY AND REQUIRE A TREMENDOUS AMOUNT OF BANDWIDTH TO TRANSMIT OVER A NETWORK

• NETWORK BANDWIDTH IS LIKE A PIPE THAT CARRIES A STREAM OF BITS.

• THE SIZE OF THE PIPE IMPOSES A LIMIT ON HOW MANY BITS CAN BE MOVED IN A GIVEN TIME PERIOD.

• MULTIPLE USERS COMPETING FOR THE SAME BANDWIDTH LIMIT THE AMOUNT OF BANDWIDTH AVAILABLE TO ANY ONE USER.

FILE SIZE AND BANDWIDTH• FILE SIZES AND BANDWIDTH REQUIREMENTS FOR

UNCOMPRESSED AUDIO CAN BE CALCULATED BY MULTIPLYING THE SAMPLING RATE BY THE RESOLUTION.

• DEPENDING ON THE NUMBER OF CHANNELS AND THE BIT-RATE, THE FILE SIZE WILL CHANGE PROPORTIONALLY.

• THE BANDWIDTH REQUIREMENT OF A DIGITAL AUDIO SIGNAL IS THE SAME AS THE BIT-RATE.

• THIS IS TRUE WHETHER THE SIGNAL IS COMPRESSED OR NOT.

Sampling Rate

Resolution

Number of

Channels

Time in Seconds

Bits/Byte File Size (in

Bytes)

44,100 *

16 *

2 *

60 /

8 =

10,584.000

FILE SIZE AND BANDWIDTH• SEVERAL THINGS CAN BE DONE TO CONTROL THE SIZE OF DIGITAL

AUDIO FILES, BUT THERE WILL ALWAYS BE A TRADE-OFF BETWEEN FILE SIZE AND SOUND QUALITY.

• LOWERING THE SAMPLING RATE PRODUCES A SMALLER FILE BUT REDUCES THE ACCURACY AND ALLOWS MORE NOISE AND DISTORTION TO BE INTRODUCED DUE TO INCREASED QUANTIZATION ERRORS.

• A MONO SIGNAL, USED IN PLACE OF STEREO WILL CUT THE SIZE IN HALF.Sampling

RateResolution Number of

ChannelsBit-rate File Size

(in Bytes)

44,100 16 2 1,411,200 10,584,000

44,100 16 1 705,500 5,292,000

22,050 16 1 352,800 2,646,000

11,025 16 1 176,400 1,323,000

11,025 8 1 88,200 616,000

COMPRESSION• LIMITED NETWORK BANDWIDTH AND HARD DISK CAPACITY HAVE BEEN MAJOR DRIVING FACTORS BEHIND THE DEVELOPMENT OF COMPRESSED AUDIO FORMATS.

• UNTIL RECENTLY, ONLY A SMALL NUMBER OF PEOPLE USE THEIR COMPUTERS TO STORE CD-QUALITY MUSIC.

• A FEW PEOPLE WOULD COPY THEIR FAVORITE SONGS FROM A MUSIC CD AND USE A CD-RECORDABLE DRIVE TO CREATE A COMPILATION CD, SIMILAR TO THE WAY MANY PEOPLE MAKE CASSETTE TAPES FROM PRE-RECORDED MUSIC.

COMPRESSION

• WITH THE MP3 ENCODED AT 128 KBPS, EACH FOUR-MINUTE SONG WOULD TAKE UP LESS THAN 4 MB OF SPACE AND COULD BE DOWNLOADED IN LESS THAN 20 MINUTES WITH A 28.8KBPS MODEM.

• A 2GB HARD DISK MAKES IT POSSIBLE TO USE A PC AS HIGH CAPACITY, CD QUALITY JUKEBOX IN PLACE OF TAPE DECKS, TURNTABLES AND CD PLAYERS.

TWO MAIN TYPES OF COMPRESSION TECHNIQUES• LOSSLESS AUDIO COMPRESSION

• THIS METHOD COMPRESSES AUDIO FILES BY CREATING AN EXACT COPY OF ONE’S AUDIO FILE.

• IT PRESERVES THE AUDIO CONTENT AND QUALITY AS IT DECREASES THE SIZE OF THE FILE

• IT DOES NOT LOSE ANY INFORMATION WHEN SOUND IS COMPRESSED

• LOSSY AUDIO COMPRESSION• RESULTS TO A LOSS OF INFORMATION OF THE AUDIO FILE

• “UNNECESSARY BITS” ARE ELIMINATED MAKING THE FILE SIZE SMALLER.

• WHEN COMPRESSED, IT CAN NO LONGER BE IN ITS ORIGINAL FORM