Behringer SRC2496 Manual - Page 9

9 ULTRAMATCH PRO SRC2496 User Manual 3.2 Sample rate conversion No matter what type of digital audio signal you feed into the ULTRAMATCH PRO, it will convert it to a common standard format. Numerous conversion examples can be found in daily studio practice: • Conversion of 48 kHz DAT recordings to the CD standard of 44.1 kHz • Conversion of older digital recordings from 44.056 kHz to 32, 44.1, 48, 88.2 or 96 kHz • Conversion of "foreign" material with 32 kHz to 44.1, 48, 88.2 or 96 kHz • Conversion of audio data with a word length of 24 bits to 20 or 16 bits for recording on a digital medium • Conversion of S/PDIF format to AES/EBU for easy mani­pulation of various parameters and improved (balanced) signal transmission • Setting or removing copy protect bits for further processing of recordings in a studio environment 3.2.1 Typical studio application with DAT Only recently has it become possible to use less expensive DAT recorders for direct recording from analog sources with a sampling rate of 44.1 kHz. Most consumer-level DAT recorders, however, record at 48 kHz. Usually, such recordings have to be transferred via an analog connection from DAT to a professional recorder. This process results in an unnecessary deterioration of the original quality of the material due to the additional D/A and A/D converters involved. With the ULTRAMATCH PRO you can eliminate this problem by converting the sampling rate purely in the digital domain, which allows for a considerably higher quality than you could achieve with analog converters. Further problems, such as incorrect formats, significantly deviating or unstable sampling rates (as long as they do not deviate by more than ±12.5% from the current sampling rate), will also be corrected by the ULTRAMATCH PRO in real time, thus ensuring the successful transfer of your audio data. 3.2.2 Hard-disk recording Hard-disk recording applications also require a uniform sampling rate, if possible the one used by the subsequent playback medium (CD). As it can convert audio material from 32, 48, 88.2 or 96 kHz to the standard 44.1 kHz, the ULTRAMATCH PRO makes sure that all sources can be used to feed audio material by way of a digital connection. Of course, the ULTRAMATCH PRO can be inserted at any point in the audio processing path, i.e. also between the PC and the DAT recorder. Therefore, with uncritical audio material you can process the material at 32 kHz in the recording system (or higher, depending on which sampling rates can be processed by the HD recording system), and subsequently convert the completely edited material while transferring it to a DAT recorder at 44.1 kHz (or even at 48 kHz). 3.2.3 Master/slave problem solver When a digital mixing console is used, it is at this point-if not earlier- that master/slave problems will be encountered. The explanation is simple: When using CD players, DAT recorder and HD recording systems in their "normal" applications, the responsibilities are clearly defined. The playback device is the master, the recording device is the slave, i.e. the CD player provides a clock rate of 44.1 kHz to which the DAT recorder is synchronized. When using a mixing console, the CD player is the master, the console is the slave. However, this model collapses all of a sudden as soon as a DAT recorder is hooked up, which does not record but plays back too. The console can synchronize to one source only, the audio data from the other source would be processed incorrectly because the two devices are not in sync. The need for synchronization in a digital studio is done justice connecting the equipment to one central sync source. For example, the console could be the master-supplying the remaining equipment with a reference signal (wordclock). However, this will only work if your other equipment has a sync input, i.e. can be used as a slave. In a studio with a digital tape machine, digital effects and hard-disk recording system it is impossible to connect commercially available CD players or DAT recorders to the mixing section of the console simply because they cannot be synchronized. By inserting the BEHRINGER ULTRAMATCH PRO SRC2496 between the equipment to be synchronized and the mixing console input, the SRC2496 can deliver the audio signal with the studio clock rate entered via the external sync input (WORDCLOCK, (20)). In this case, the ULTRAMATCH PRO works as intermediate gear of sorts, whose toothed transmission always ensures that there is an appropriate gap in the gearwheel. It synchronizes the signal coming from the devices to be synchronized, while converting to the desired sampling rate in compliance with the wordclock signal. In a studio with a central clock generator, it is therefore possible to use the ULTRAMATCH PRO to connect any unit to any other, regardless of any other options available. ◊ Even if the central clock does not correspond exactly to one of the sampling rates, the ULTRAMATCH PRO will assign a corresponding marker to the output signal! This marker depends on the automatically detected and displayed sampling rate, which is important because DAT recorders usually "refuse" to enter record mode if an incorrect sampling rate has been indicated. 3.2.4 Bridging unformatted passages DAT recorders, in particular, produce tiny format gaps between individual recorded passages on the tape when intermittent recordings are made. Also, when you transfer older recordings it can happen that short passages with a different sampling rate than that of the current recording remain stored on tape. In such cases, the ULTRAMATCH PRO converts this host of single pieces of information into a continuous data stream with a fixed sampling rate. Even if the DAT recorder or any other digital source is stopped or switched off, the ULTRAMATCH PRO will continue to generate a continuous signal (depending on the digital signal, if synchronized to it). 3.3 Removing copy protect information The original copy protect mechanism used in DAT recorders was simple but effective: It was impossible to make digital recordings from a CD. Later, a step-by-step mechanism was introduced with SCMS, which allowed at least for one digital copy from CD. The routine implemented in SCMS depends on the generation (xth copy) and the origin (category) of the digital audio material. In professional studio engineering a copy protect mechanism does not make any sense, which is why there is none defined in the AES/EBU standard. Since many studios use inexpensive consumer devices for cost reasons, copy protect and/or format incompatibility problems (professional/consumer) are encountered frequently. The SRC2496 can ignore all types of copy protect information and generate a new, completely free marker that allows for multiple copying. Thus, you can use your ULTRAMATCH PRO to copy material from one consumer DAT to another. Further information on this subject can be found in chapter 2.1.3, section (28). 3.4 Noise reduction with emphasis A very special feature is the option to influence the set emphasis bit. "Emphasis" here means a noise reduction process with a treble boost step involved prior to recording. This treble boost is undone during playback. A specific bit (emphasis bit) in the digital data stream contains the information whether or not the signal has been processed with this technique. It is however NOT a modification of the audio signal, but only of the emphasis marker contained in the digital data stream.