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Digital Recording

Date post: 05-Jan-2016
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Digital Recording. Digital recording is different from analog in that it doesn’t operate in a continuous way; it breaks a continuously varying waveform into a sequence of individual amplitude assessments called samples. - PowerPoint PPT Presentation
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Digital Digital Recording Recording
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Page 1: Digital Recording

Digital RecordingDigital Recording

Page 2: Digital Recording

Digital recording is different from analog in that it doesn’t operate in a continuous way; it breaks a continuously varying waveform into a sequence of individual amplitude assessments called samples.

Page 3: Digital Recording

Samples are energy readings that occur several times per second. A greater number of readings will yield a recording that is closer to reality.

Page 4: Digital Recording

Advantages to digital Advantages to digital recording over analog:recording over analog:

excellent signal to noise ratio (no tape excellent signal to noise ratio (no tape hiss) hiss)

copies can be as good as the originalcopies can be as good as the original data can easily transferred between data can easily transferred between

various types of mediavarious types of media data storage is relatively inexpensivedata storage is relatively inexpensive data storage is accurate and relatively data storage is accurate and relatively

reliablereliable

Page 5: Digital Recording

Advantages: continuedAdvantages: continued

data is easily manipulated (cut, copy, data is easily manipulated (cut, copy, paste…etc.)paste…etc.)

locating musical sections is locating musical sections is instantaneous (No rewind time) instantaneous (No rewind time)

sound quality of the recording does not sound quality of the recording does not degrade with each recording take.degrade with each recording take.

The technology is relatively affordable. The technology is relatively affordable.

Page 6: Digital Recording

Digital Audio TheoryDigital Audio Theory

In the world of digital In the world of digital recording the information is recording the information is encoded as a series of “0”s encoded as a series of “0”s and “1”s. Data is represented and “1”s. Data is represented by a series of binary data that by a series of binary data that is referred to as is referred to as Pulse Code Pulse Code Modulation (PCM)Modulation (PCM)..

Page 7: Digital Recording
Page 8: Digital Recording

The quality of a digital The quality of a digital recording is determined by recording is determined by twotwo main factors: main factors:

Sample rate (horizontal Sample rate (horizontal resolution) resolution)

Bit resolution (vertical resolution) Bit resolution (vertical resolution)

Page 9: Digital Recording

4 Bit Sample

Page 10: Digital Recording

A) Sample rate A) Sample rate (horizontal resolution)(horizontal resolution) The process of The process of sampling sampling (digital encoding and (digital encoding and

decoding) breaks the time axis (horizontal) and decoding) breaks the time axis (horizontal) and voltage axis (vertical) into a specific number of voltage axis (vertical) into a specific number of steps. At each step along the time axis a steps. At each step along the time axis a measurement is taken of voltage (amplitude) measurement is taken of voltage (amplitude) status. The status. The sample rate sample rate is the number of times is the number of times per second that the processor samples the per second that the processor samples the voltage (amplitude) of an analog waveform. voltage (amplitude) of an analog waveform.

Page 11: Digital Recording

The Nyquist Theorem states that in order to accurately sample a sound, the sample rate has to be at least twice the desired highest frequency. Therefore, to accurately and faithfully reproduce a frequency of 20 000 Hz (the upper range of human hearing) the sample rate must be at least (2 x 20 000 Hz) or 40 000 Hz.

Page 12: Digital Recording

This is why the standard audio CD sample rate was fixed at 44 100 Hz (44.1 kHz). Most people feel that 44.1 kHz is an ample sample rate to capture the frequencies inherent in recorded sound. However, recording engineers and physicists know that sound perception involves more than just distinguishing frequencies

Page 13: Digital Recording

Stereo localization of Stereo localization of soundsound

Frequency perception of a sound is complicated Frequency perception of a sound is complicated somewhat by the fact that we have somewhat by the fact that we have two earstwo ears. Our . Our brains perceive sounds on a three-dimensional plane. brains perceive sounds on a three-dimensional plane. This concept is sometimes referred to as This concept is sometimes referred to as triangulationtriangulation. .

The brain localizes sound by calculating the time delay The brain localizes sound by calculating the time delay difference between the arrival of a sound at each ear difference between the arrival of a sound at each ear ((Haas effectHaas effect). 15 microsecond time differences are ). 15 microsecond time differences are discernible by almost everybody. Some people can discernible by almost everybody. Some people can even perceive time differences as little as 5 even perceive time differences as little as 5 microseconds between ears. microseconds between ears.

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Because we perceive these small time differences between ears, the current standard sampling rate of 44.1 kHz is really not enough to deliver the level of stereo localization that our ears demand.

Page 15: Digital Recording

At a sampling rate of At a sampling rate of 44.1 kHz44.1 kHz the samples are the samples are 23 microseconds23 microseconds apart. apart.

At a sampling rate of At a sampling rate of 48 kHz48 kHz the samples are the samples are 20 20 microsecondsmicroseconds apart. apart.

At a sampling rate of At a sampling rate of 96 kHz96 kHz the samples are the samples are 10.417 microseconds10.417 microseconds apart. apart.

At a sampling rate of At a sampling rate of 192 kHz 192 kHz the samples are the samples are 5.2085.208 microseconds apart. microseconds apart.

Page 16: Digital Recording
Page 17: Digital Recording

THE FUTURE?THE FUTURE?

It is believed that someday 192 It is believed that someday 192 kHz will likely be the standard kHz will likely be the standard sampling rate for all professional sampling rate for all professional sound recording.sound recording.

Page 18: Digital Recording

B) B) Bit Resolution Bit Resolution (vertical resolution)(vertical resolution)

At each sample point, signal strength At each sample point, signal strength (amplitude) is calculated. The sample (amplitude) is calculated. The sample strength is measured against a discrete strength is measured against a discrete number of vertical increments. To number of vertical increments. To achieve greater precision in resolution achieve greater precision in resolution requires that we aim for a greater number requires that we aim for a greater number of vertical increments. of vertical increments.

Page 19: Digital Recording

CD’s are recorded at a 16 bit resolution. This means that each bit has a word length of at least 16 digits (example: 0101110111010101).

A greater the number of digits in a bit-word provides a more precise vertical measurement of signal strength.

Page 20: Digital Recording

There is a simple formula to calculate the number of vertical increments if we know the length of the bit word.

If “n”= the length of the bit word (bit resolution).

2ⁿ = number of vertical increments

Page 21: Digital Recording

Let’s use the formula to calculate the number of vertical increments for a standard 16 bit resolution CD audio

recording.

216 = 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2

= 65 536 vertical increments

Page 22: Digital Recording

Because bit resolution uses an exponential formula even a small increase in bit rate offers a significant increase in resolution.

Page 23: Digital Recording

The table below should give you a pretty good idea:

Bit resolution Vertical increments

8 256

16 65 536

18 262 144

20 1 048 576

24 16 772 216

Page 24: Digital Recording

Computer soundcards and audio interfaces with the capability for 24 bit resolution and 192 kHz sampling rates are currently available.

This will likely become the standard for all professional audio recording in the next few years.

Page 25: Digital Recording
Page 26: Digital Recording

Keep in mind that when we increase the sample rate and bit resolution we are also increasing the amount of data that the computer has to manage.

When assembling a computer for professional audio work it is important to aim for a fast processor, a large/fast hard drive and, most importantly, lots of RAM.

Page 27: Digital Recording
Page 28: Digital Recording

Digital Audio FormatsDigital Audio Formats

CompressedCompressed: :

MP3, MP4, WMA, ATRAC, RA, RAM, MP3, MP4, WMA, ATRAC, RA, RAM, OGG,FLAC, AAC ….and the list goes on !OGG,FLAC, AAC ….and the list goes on !

UncompressedUncompressed::

WAV (Windows) , AIFF (Apple) , AU (Sun)WAV (Windows) , AIFF (Apple) , AU (Sun)

Page 29: Digital Recording

Consumer digital Consumer digital playback devices:playback devices:

CD playersCD players DATDAT ComputersComputers Mini DiscMini Disc iPods and Mp3/WMA file playersiPods and Mp3/WMA file players Super-Audio CD players (SACD)Super-Audio CD players (SACD) DVD-AudioDVD-Audio BLU-Ray or HD-DVD …future?BLU-Ray or HD-DVD …future?

Page 30: Digital Recording

Final Thoughts !Final Thoughts !

Artists are currently recording and Artists are currently recording and mixing their music at increasingly mixing their music at increasingly higher sample resolution and bit higher sample resolution and bit rates. They can even make a mix in rates. They can even make a mix in 7.1 channel surround sound. 7.1 channel surround sound.

The problem is that most listeners The problem is that most listeners are not really concerned with the are not really concerned with the actual sound quality of their music. actual sound quality of their music.

Page 31: Digital Recording

If sound quality not really If sound quality not really a priority, what is?a priority, what is?

cost?...freecost?...free

speed and efficiency of deliveryspeed and efficiency of delivery

storage spacestorage space

portabilityportability

wide selection of choiceswide selection of choices


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