Image and Sound Editing

Raed S. Rasheed2012

Digital Sound

• Digital sound types– Monophonic sound– Stereophonic sound– Quadraphonic sound– Surround sound

• Digital sound depth• WAV PCM sound file format• Audio sine wave• Amplifying digital sound• Reduce digital sound

Digital sound types

• Monophonic sound:– Commonly called mono sound, mono, or non-

stereo sound, this early sound system used a single channel of audio for sound output. In monophonic sound systems, the signal sent to the sound system encodes one single stream of sound and it usually uses just one speaker. Monophonic sound is the most basic format of sound output.

Digital sound types

• Monophonic sound:

Digital sound types

• Stereophonic sound:– Commonly called stereo sound or just stereo,

stereophonic sound divides sounds across two channels (recorded on two separate sources) then the recorded sounds are mixed so that some elements are channeled to the left and others to the right. Stereophonic sound is generally considered the best sound technology of the 1950 and early 1960's.

Digital sound types

• Stereophonic sound:

Digital sound types

• Quadraphonic sound:– Quadraphonic sound uses four channels to output

sound; right front, left front, right rear, and left rear. The goal of a quadraphonic sound system is to reproduce sounds in both the front and back of the listener, which simulates 360-degree sound. Quadraphonic sound became the more common and popular choice in the late 1950s to early 1960s versus Four Channel Discrete which was also available during that time.

Digital sound types

• Quadraphonic sound:

Digital sound types

• Surround sound:– Surround sound is a term used to describe a type of

audio output in which the sound appears to "surround the listener" by 360 degrees. Surround sound systems use three or more channels and speakers in front and behind the listener to create a surrounding envelope of sound and directional audio sources. The term surround sound has become popular in recent years and more commonly used since the advent of home theater systems. Surround sound can be either an analog or digital system.

Digital sound types

• Surround sound:

Digital sound depth

• Bit depth describes the number of bits of information recorded for each sample. Bit depth directly corresponds to the resolution of each sample in a set of digital audio data. Common examples of bit depth include CD quality audio, which is recorded at 16 bits, and DVD-Audio, which can support up to 24-bit audio.

Digital sound depth• An audio file's bit rate can be calculated given sufficient information.

Given any three of the following four values, the fourth can be calculated.– Bit rate = (sampling rate) x (bit depth) x (number of channels)– E.g., for a recording with a 44.1 kHz sampling rate, a 16 bit depth, and 2

channels (stereo):– 44100 x 16 x 2 = 1411200 bits per second or 1411.2 kbit/s– The eventual file size of an audio recording can also be calculated using a

similar formula:– File Size (Bytes) = (sampling rate) x (bit depth) x (number of channels) x

(seconds) / 8– E.g., a 70 minutes long CD quality recording will take up 740880000 Bytes,

or 740MB:– 44100 x 16 x 2 x 4200 / 8 = 740880000 Bytes

WAVE PCM sound file format

Resource Interchange File Format

WAVE PCM sound file formatAs an example, here are the opening 72 bytes of a WAVE file with bytes shown as hexadecimal numbers:52 49 46 46 24 08 00 00 57 41 56 45 66 6d 74 20 10 00 00 00 01 00 02 00 22 56 00 00 88 58 01 00 04 00 10 00 64 61 74 61 00 08 00 00 00 00 00 00 24 17 1e f3 3c 13 3c 14 16 f9 18 f9 34 e7 23 a6 3c f2 24 f2 11 ce 1a 0d

Audio sine wave

• All waves have certain properties. The three most important ones for audio work are shown here:– Wavelength: The distance between any point on a

wave and the equivalent point on the next phase. Literally, the length of the wave.

Audio sine wave

– Amplitude: The strength or power of a wave signal. The "height" of a wave when viewed as a graph. Higher amplitudes are interpreted as a higher volume, hence the name "amplifier" for a device which increases amplitude

Audio sine wave

– Frequency: The number of times the wavelength occurs in one second. Measured in kilohertz (Khz), or cycles per second. The faster the sound source vibrates, the higher the frequency. Higher frequencies are interpreted as a higher pitch. For example, when you sing in a high-pitched voice you are forcing your vocal chords to vibrate quickly.

Audio sine wave

Amplifying digital sound

• Amplify the signal to an audible level by multiplying it by a constant.

ALGORITHM Sound_IncreaseVolume 5.101 INPUT Sound, c02 OUTPUT NewSound03 BEGIN04 Create new sound file NewSound;05 For each sample06 SET NewSound(sample) = Sound(sample) * c;07 END For08 RETURN NewSound;09 END

Reduce digital sound

• Reduce the signal to an audible level by dividing it by a constant.

ALGORITHM Sound_DecreaseVolume 5.201 INPUT Sound, c02 OUTPUT NewSound03 BEGIN04 Create new sound file NewSound;05 For each sample06 SET NewSound(sample) = Sound(sample) * c;07 END For

08 RETURN NewSound;09 END

Combine digital sounds

ALGORITHM Sound_Combination 5.301 INPUT Sound1, Sound202 OUTPUT NewSound03 BEGIN04 Create new sound file NewSound;05 For each sample1 in Sound106 SET NewSound(sample1) = Sound1(sample1);07 END For08 For each sample2 in Sound209 SET NewSound(sample1+sample2) = Sound2(sample2);10 END For11 RETURN NewSound;12 END

Combine digital sounds

ALGORITHM Sound_Combination 5.401 INPUT Sound1, Sound202 OUTPUT NewSound03 BEGIN04 Create new sound file NewSound;05 For each sample in Sound1, Sound206 SET NewSound(sample) = Sound1(sample) + Sound2(sample);07 END For08 RETURN NewSound;09 END