Is there an advantage of SCSI over IDE for digital recording?
There is a widespread belief among audio workstation users, both at home and in the studio, that only SCSI drives can provide the required performance.
However, despite a number of obvious advantages of SCSI, most of the professional workstations on the IBM PC can easily work with IDE disks. The read / write speed of typical IDE disk models today (late 1998) is in the 6-10 Mb / s level with a seek time of approximately 8-10 ms, which is equivalent to the same typical SCSI models (not high-end).
Such a hard disk can easily cope with the simultaneous reading of 16-bit audio data in 20-30 audio channels at a sample rate of 48 kHz and slightly less data in the case of recording. Another thing is that in the case of SCSI, its internal optimization (ordering requests to minimize head movement in SCSI-2) often masks the suboptimal performance of the operating system and sound program, and to achieve this level, an IDE may require a good operating system driver and a well-made program (eg DDClip).
The reasons for the dislike of many users for IDE disks are due to the fact that they generally find these disks in cheap, poorly assembled and tested average power computers consisting of varied components that are often poorly compatible with each other. In contrast, SCSI drives are often installed in more powerful and expensive models that contain components from “respected” manufacturers, more carefully assembled and tested. Replacing the SCSI disk in the second version with an IDE disk of approximately the same performance and assembling / configuring the system with the characteristics of IDE in mind in many cases will not have a noticeable effect on its performance.
Why are AV hard drives used in digital recording?
The class of AV (Audio / Video) hard drives stands for their ability to record and read streams of data extremely smoothly, without gaps. These disks are equipped with a larger internal buffer and do not interrupt the read / write process through thermal calibration of the positioning system. For digital recording systems that lack the speed and RAM capacity to smooth out potential irregularities in performance of conventional discs, AV discs are the only option.
It should be noted that the presence of the abbreviation AV in the designation of the disc does not mean that it belongs to the Audio / Video class; this must be clearly mentioned in the disc’s passport.
However, this feature is generally needed only when working with high-quality video information, the reception rate of which is approximately 10 megabytes per second per channel. For sound systems, the speed of a single channel 16-bit stream with a sample rate of 48 kHz is two orders of magnitude lower, amounting to just 94 kilobytes per second. At the same time, almost no workstation is capable of providing simultaneous work with hundreds of channels, just as a hard disk cannot simultaneously process such a large amount of data located in different parts of it. In real multi-channel recording applications to a disc, most of the overhead of the disc subsystem falls on the movement of the heads between the recording sections and in no way on the data transfer itself. The low speed of audio streams makes it more convenient and reliable to store them in the computer’s RAM, which compensates for the thermal calibration of the disk within 0.5 – 1 s, instead of using expensive and rare AV-class disks . Furthermore, thermal calibration does not have a noticeable effect on the uniformity of the data stream on not all conventional disks.
“Irregular” data transfer can also occur when using the “wrong” operating system (DOS, Windows without a 32-bit disk driver, etc.), insufficient number and size of operating system file buffers and the recording program, using low-class drives with a transfer rate of the order of 1-2 megabytes per second or less, wrong disk connection, etc. In either case, these situations usually indicate an incorrect configuration of the system hardware and software.
