Digital Audio - Hard Disc Recording

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Hard Disc Recording (from now on HDR) means using a computer for the manipulation of sound signals. Since we're speaking of computers, this technique has also undergone a full-scale revolution over the past few years, to the point that they have become an ever-increasing alternative to analogue recording. Through audio data-capture cards, the analogue signal is converted into digital; the quality of its conversion depends on the card's characteristics, both in terms of sound quality and in terms of performance. The data produced by the sound card is stored on a magnetic support, the computer's HD (which is usually an external unit which fulfils this duty, and whose bit-rate, namely its data-transferring rate, is very high) and at this point the signals are ready to be manipulated to obtain the desired result. In order to do this our computer shall be equipped with an appropriate software which is capable of managing all the operations we need to carry out on the signals.

The card that converts the signal from analogue to digital and from digital to analogue should be located outside the computer itself, and is the HDR interface for the external world. Seeing that the sampling process produces large amounts of data, we need an appropriate support for it and a very quick access time. Within the computer we have the DSP (Digital Signal Processing) unit that elaborates the signals, because a normal computer wouldn't be able to process such a massive amount of data[37 ]. So, our DSP card will take care of carrying out all necessary elaborations on the signal, whilst allowing the computer that hosts it to be free to fulfill its normal duties. That's why an HDR system doesn't necessarily require a computer with extraordinary performances, what matters is the DSP card's power. With computers, the only characteristic that always fits the motto "the more the better!" is the amount of available RAM memory. This is because RAM is a type of memory that allows a much faster access to data than the Hard Disc and therefore the operations that are carried out on the data within it are much faster. In actual fact, the operations that are carried out on the HD data also need to take place in the RAM, but before this can take place, the data needs to be transferred from the HD to the RAM resulting in a considerable loss of time: the larger the RAM the less often we need to transfer the data from the HD.



[37 ] In this context we're referring to professional HDR systems in which the quality cannot be below a certain limit. For a more recreational use, normal computers with normal sound cards (or ideally slightly more sophisticated cards) are more than sufficient. In this case the DSP processing is usually carried out by the computer's CPU.








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