5.6.6 Replay Equipment
5.6.6.1 There are two fundamentally different approaches to reproduction of audio CD and DVD sources: traditional replay using format-specific reproduction equipment; or digital audio extraction (DAE) using a general purpose CD-ROM or DVD-ROM drive, commonly referred to as “ripping” or “grabbing”. The chief advantage of the data capture or ripping method is greater speed, for while traditional reproduction requires transfer in real time, data capture or “ripping” utilising high speed drives can easily transfer audio data in less than one tenth of the actual audio running time.
5.6.6.2 Digital Audio Extraction: The chief disadvantage of DAE is in error handling. The simplest “ripping” software has no error correction capability at all. More sophisticated systems make some attempt at error management but do not have the functionality to fully implement the error checking, correction and concealment that is necessary for accurate transfer, and which is built into format specific equipment. Top end professional systems promise error handling equivalent to the format specific approach, yet few have accurately implemented it.
5.6.6.3 Reproduction at rates significantly faster than real time are desirable in that this reduces the resources required to transfer audio material to the target archival system. If the DAE system can be automated, this has the added advantage of freeing staff resources for the more human resource intensive tasks of converting analogue audio to digital. Automated systems can be used appropriately if there is no loss of accuracy in the transfer process. In fact, in the better systems, there is less danger of data inconsistencies, particularly those affecting metadata but also possibly affecting the content itself.
5.6.6.4 Reproduction of digital audio data should always be accompanied by an accurate error detection and recognition system that describes and identifies exactly the kind and number of CD-specific errors and associates them with the metadata specific to that audio file. This is all the more critical where automated, faster-than-real-time processes are used to acquire the audio data.
5.6.6.5 The reproduction of an audio CD is a unique process where a somewhat subjective decision needs to be made about the success, or otherwise, of the transfer process. Unlike the transfer of audio data files, this decision can only be made by considering the error protocol. Data formats, such as .wav or BWF, can be objectively checked by bit for bit comparison between the new and old files. CD audio is not a digital file, but a coded stream of audio data, a significant difference when it comes to managing the audio integrity.
5.6.6.6 Systems which guarantee error detection and recognition including error protocol in a faster- than¡real-time mode up to a maximum of 12 times, relative to real time audio replay, are available on the market and are generally specifically aimed at the archival market.
5.6.6.7 The minimum requirement for archival use of DAE is that the DAE system must detect and alert the operator to any digital audio errors.
5.6.6.8 Format Specific Replay Approach: To transfer a CD encoded in CD-A format a stand-alone CD player may be used. The required replay equipment is a CD player with digital output, permitting ingest of the digital audio stream via a sound card with digital input. Preferred interface standard for the digital audio stream is AES/EBU. Use of the SPDIF interface can provide the same results but cable runs must be kept short. Any conversion between AES/EBU and SPDIF needs to accommodate the differences between the two standards, notably the different use of status bits that carry emphasis and copyright flags (Rumsey and Watkinson 1993). The disadvantage with this real time replay approach is that it is very time consuming, and no record of error correction is maintained in the record metadata.
5.6.6.9 Sound cards for ingest of CD audio must accommodate two channels at 16 bit 44.1 kHz. Replay equipment should be of commercial quality. Care taken in ensuring a stable vibration free mounting for the player will ensure maximum reliability of replay.
5.6.6.10 The CD player must be in good replay condition. In particular, optimum laser power is mandatory, and the laser lens should be cleaned from time to time. Devices such as disc-tuners are of no use to any replay of a CD. It is advised against using protective foils (so called CDfenders/ DVDfenders) because they may come off from the disc and damage the drive2.
2. CDs aus dem Kuhlschrank. Funkschau no. 23, 1994, p.36-39. The effect of improving the replay quality of CDs or DVDs by cooling them down in a refrigerator is so minute that though it was shown in theory (mathematically) it has never been shown in practice
