In digital recording, digital video and digital audio are straightforwardly recorded to a data storage item in the form of flow of discrete numbers that demonstrate the changes occurring in air pressure for audio, luminance values and chroma for video at a time. Consequently, an abstract template for the moving image or original sound should be done.
Starting from 1980s, the SPARS code was applied for specifying music that had to be recorded, mastered and mixed in a digital form. This code identified whether one or another process was analog or digital.
In 1937, Alec Reeves who is a scientist from Great Britain took out a patent for Pulse-code modulation describing. Bell Telephone Laboratories designed the first digital scrambled speech transmission system in 1943. Employer of Bell worked out the system of recording sound through the computer in a digital form in 1957. 1967 was marked by the invention of the first digital audio recorder equipped with magnetic tape. It’s a 12-bit 30 kHz stereo device that uses a compander in order to widen dynamic range. James Russell took out a patent for the first digital-to-optical recording system in 1970. A compact disc was developed on the basis of this system. Thomas Stockham made the first digital audio recordings by means of standard computer devices and created a digital audio recorder according to his design. It was the first recorder that was commercially available. Stockham’s Soundstream company offered it. Denon developed 8 track reel for reel digital recorder in 1972. Sound 80 Records of Minneapolis makes recording on “Flim and the BB’s” straightly in a digital form before the viny1 LP in 1978. has been pressed. Bob Berglund was the mastering engineer. A 3M Digital Audio Mastering System played a role of a recording system. The prototype of digital compact disc was developed in 1979. It was a mix of perfect sound quality and medium size. In 1979, Warner Bros. Records introduced the album of music written by guitarist Ry Cooder that had been firstly recorded in a digital format. 3M corporation manufactured 32 track digital machine. And mentioned album was made with its use. Sony and Philips started to sell the first digital compact discs in 1982. Also, New England Digital made available the hard disk recorder feature on the Synclavier which was first commercial hard disc recording system. In 1982, Peter Gabriel introduced Security, the first complete digital recording. Digital radio started to broadcast in Canada by means of the L-Band in 1990.
Alesis Digital Audio Tape (ADAT) is famous as a tape format that is suitable in order to record 8 tracks of audio in a digital format at a time onto Super VHS magnetic tape. This format resembles the format that consumer VCRs employ. The new development was pronounced at the NAMM convention in Anaheim, California in 1991. The ADAT recorders were launched in February 1992. DVD players and optical discs came into the market in Japan in 1996.
It’s necessary to clarify what the procedure of recording is. Analog signal is conveyed from the data-input unit to an analog-to-digital converter or ADC. In turn, the ADC transforms received signal. It is made in such a way: the momentary level of the analog audio wave is systematically sized and after this a binary number which has a pre-determined number of bits, which is called a word length, is designated to every measuring point. Sample rate, also called sampling rate, is frequency at which the ADC sizes the level of the analog wave.
A digital audio sample which has a pre-determined word length identifies the audio level at one given moment. Exactness of the initial audio wave representation depends on the word length. So the long word length makes the wave representation better. High sampling rate raises the upper cutoff frequency of the digitized audio signal. The ADC sends out a sequence of samples which generates a continued stream of 0s and 1s. Recording media is a place of storage of mentioned numbers. Variety of media includes optical drive, hard drive, solid state memory and magnetic tape.
It’s also necessary to clarify the essence of playback. The sequence of numbers has to be conveyed from storage to a digital-to-analog converter, or DAC. This converter retransforms these numbers to an analog signal. For this, the level information that is kept in every digital sample has to be stuck together. In such a way the initial analog wave form is rebuilt. The signal is boosted and conveyed to the video screen or loudspeakers.
Once the signal has been transformed to bits, it doesn’t mean that it’s easy to record it. The most difficult thing is to determine a method by means of which it will be possible to record the bits at the speed that is suitable for maintaining the signal. For instance, in order to record 2 channels of audio at 44.1 kHz sample rate with a 16 bit word size, the recording program has to process 1,411,200 bits per second.
If commercial media has to be recorded, it’s necessary to know some techniques. In case of a digital cassette, the tape and the read/write head move for handling speed at the level which is suitable in order to sustain the bits at a well-handled size. In case with optical disc recording equipment, such as DVDs and CDs, microscopic holes into the dye layer of the medium are burnt by means of a laser. These signals are read by means of a weaker laser. This is possible, as the disc metallic substrate has the reflective coating. The unburned dye impedes reflection, but the holes in the dye promote it. This enables representation of digital data.
There are some issues concerning digital audio recording that have to be considered. Word size is one of them. The approachable noise level of a signal that is recorded with a distortion of an signal without dither, or with added dither, is straightly influenced by the quantity of bits which are used for the representation of a single audio wave, also called a word size. The increase of the word length of a sample by one bit double-strengthens its potential benefits, by analogy with the increase of the eventual accurateness of each sample and the fidelity of the recording to the original. As a rule, 24-bit recording is regarded to be an existing practical limitation, because such a word length lets a signal-to-noise ratio to exceed the most analog circuitry. There is a demand to use it in at the very minimum 2 points in the recording/playback chain.
Sample rate refers to another issue. By its significance, sample rate even exceeds word size. Reconstruction of the sampled signal to the initial sound signal is impossible in case that a sample rate is very low. Consequently, the output will differ from the input. Undersampling process leads to aliasing and the high frequency elements of the sound wave are submitted at lower level than they have to be. As a result, the shape of the output wave is considerably changed.
For overwhelming aliasing, the sound signal, and also any other signal, must be selected at a rate at the very minimum two times of the highest frequency component in the signal. It has the name of Nyquist-Shannon sampling principle.
In order to record audio of music quality, there is a range of the most widespread PCM sampling rates. They are 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, and 192 kHz.
When professional audio recording and mastering developers make a recording, they usually make a master recording at as high sampling rate as possible. After this editing and mixing are made at the same high frequency. PCM recordings with high resolution are written down on DVD-Audio that is also called DAD, DVD-A, Blu-ray and DualDisc. Currently, it’s also a widespread practice to write down a high resolution record straightly as a lossless compression format like FLAC, generally at 24 bits, and uncompressed WAV file. And it’s not necessary to downconvert it. But if it’s required to utilize a recording for making a CD, such an approach has to be used: the initial recording has to be made with employing of a sampling rate of 44.1 kHz. There is one more popular approach, the essence of which is to utilize a higher sample rate and after this downsample a file to the determinate sample rate of the format. As a rule, this is one of the stages of the mastering procedure. This approach is beneficial, because it allows to write down a high resolution record, a CD and lossy compressed file, like mp3. All of them are made from a given master recording.
Comparing to analog recording, digital one is beneficial due to its fault tolerance.
