There are many rumors and stories about how and when the first audio recording was done. Nevertheless Thomas Edison is reckoned as the pioneer in this field: on December 6, 1877 he recited the first stanza of the poem “Mary had a little lamb” on his tinfoil phonograph.
Since then many different formats were created to record and playback audio, such as the gramophone disc, the compact cassette, DAT, the MiniDisc etc. In the meantime digital hard disc recording has become the standard.
Analogue Signals
For all kinds of storing, the audio signal needs to be converted into an electrical signal. The electrical audio signal reflects the wave of the sound. With an analogue signal a continuous voltage is conveyed. Such an electrical audio signal can easily be modulated onto a gramophone disc or a magnetic tape. A physical quality in a medium, such as the intensity of the magnetic field or the path of a record groove, is directly related, or analogous, to the physical properties of the original sound.
Digital Signals
Digital recording means converting an electrical analogue signal into a digital signal. The most important characteristics of a digital signal are the sampling rate and bit depth. In general, the conversion from analogue to digital involves taking periodic measurements or samples of the audio signal level and translating those measurements into a string of 0’s and 1’s. Expressed graphically this can be described as transferring a sine wave into a “stair” wave (see graph below).
Sampling Rate
The sampling rate describes how many times per second the analogue signal is measured. The higher the sampling rate the higher the possible maximum frequency response. A sampling rate of 44.1 kHz (the analogue signal is sampled 44,100 times per second) can accommodate audio frequencies as high as 22,050 Hertz, delivering “CD quality.” Lower sampling rates provide reduced sound quality (sometimes described as “speech quality“) but results in smaller file sizes and faster download speeds.
Higher sampling rates are sometimes found on professional recording equipment, although there is debate as to whether sampling rates much higher than 44.1 kHz translate into audible improvements in sound quality.
Bit Depth
The bit depth describes the number of digital bits used to store the measurement of the audio signal level each time it is sampled. Using more bits allows a more accurate measurement and a better quality recording, by increasing the dynamic range and reducing hiss.
For example, an 8-bit sample allows the audio signal level to be measured in 256 discrete steps; if the actual signal level is somewhere between two steps, then the estimate won’t be accurate. A 16-bit sample (used on audio CD’s) allows 65,536discrete steps, which is enough to create a very accurate estimate of the signal.
Using more bits (e.g. 24-bit which are 16 million steps, or even 32-bit which are 4,300 billion steps) also results in larger file sizes and longer download times, however, this requires more processing power and memory when editing. The resulting digital signal can be stored on different media such as CDs, DAT tapes of directly onto a hard disk.
