Digital Recording
The sound recorded by electrical equipment can be converted to a digital format.
What does digital mean? A digital circuit board within a computer is still an electric circuit board. However, it will not process continuous, electric voltage levels. Rather, at its most basic the circuit will either have an electrical charge to process or there will be no electrical charge to process. There can only be an “on” state or an “off” state at any given point in time (discrete). This two choice option of on or off can be symbolic of the number one and zero. This two choice number option is what makes up the binary numbering system. The binary system is capable of an infinite amount of numbers or can also substitute for the decimal or hexidecimal numbering system. Thus, to say that data, a circuit or a computer is digital is to say that it processes this finite, two option set of data at a specific moment. This two option binary choice can also represent a “true” or “false” statement of logic. By placing many circuits in sequence or parallel to each other, the series of ON / OFF, OPEN / CLOSE, TRUE / FALSE can represent “AND” “OR” symbolic logic. By assigning each binary digit, or group of binary digits, to represent a letter or number, complex equations can be created, broken down into their most basic components and manipulated into a new complex equation.
Digital data can be represented by the presence or absence of an electrical charge, or it can be represented by the length of time between the pulses of the charge, by the presence or absence of light pulses in a fiber optic cable, by pits and grooves in a plastic CD, by the presence and absence of sound carried over a copper telephone wire, or by the frequency of the data set when modulated into a radio frequency. By reducing the real world analog state to the digital state, we can create accurate models of the analog state, manipulate the data as a mathematical equation and store the information in a manner that is not easily subject to dissipation or degradation. Any data such as audio, film, graphics, telephone signals, text, video and radio waves can be rendered in a digital representation or format.
A microphone may be placed in front of an instrument or other sound source and the microphone cable can be connected to the back of a computer (depending on the soundcard), DAT recorder or to a digital mixer / sampler. Any instrument or any sound source can be saved in a digital form and saved to the hard disk of a computer. The computer or digital device contains an Analog to Digital Converter (ADC), which is a circuit board and specific software program application that processes the incoming continuous, electric analog signal.
- As the continuous, electric analog, varying voltage signal flows to the ADC it is deconstructed into component sine waves (by frequency) and then reconstructed.
- The signal is usually then routed through a low pass filter to set a maximum frequency that the ADC program application will accept and all other frequencies higher than the set value are eliminated.
- The ADC then selects a point on the continuous, electric analog signal to convert to a digital value (sample point).
- The amount of points selected by the ADC is based on a predetermined rate of selected points per second (Sampling Rate).
- A sample-and-hold circuit will hold the selected point on the electric analog signal.
- A small amount of predetermined analog signal is added to the sample analog signal (Dither) so that when the digital sample is produced, which is a finite number representation, it will more accurately reflect the original curved sine waveform.
- The ADC assigns a bit-value to each electric voltage analog signal that has been selected, which describes the electric voltage amplitude level of the selected point at that given moment as binary, numeric data. Thus, the constant voltage analog signal is converted into discrete steps of voltage.
- The digital signal bit stream produced by each sample produced by the ADC is then passed through a second filter (this time digital) to smooth out those periodic samples per second as they were discrete/finite and not a continual flow like the original electric analog signal.
- The digital information is first processed into the computer’s RAM and can then be stored on a drive either in the mixer / sampler or the computer. Thus, Digital Recording and Sampling are essentially the same function.