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Apogee AP8AD & AP8DA

A-D & D-A YGDAI Converter Cards
By Hugh Robjohns

If you're happy with the facilities of your Yamaha console or recorder, but you just want to upgrade the quality of the A-D/D-A conversion, these two cards from Apogee might be just what you're after.

The products of American A-D conversion specialist, Apogee, represent to many the state of the art when it comes to translating audio signals between the digital and analogue domains. The company has also been involved in making upgrade products to improve the performance of digital equipment since the very beginning of the digital age. Does anyone remember the replacement anti-alias and reconstruction filter blocks for the pioneering Sony PCM1600 series machines, for example?

Apogee AP8AD & AP8DA converter cards.Of course, digital conversion technology has come a very long way indeed in the last twenty years or so, but Apogee have always remained at the cutting edge, both in the design and manufacture of their own stand-alone converter products, and in the provision of upgrades for products from other manufacturers. It is the latter which concerns us here, since this review is of a pair of plug-in cards designed to enhance a wide range of Yamaha digital mixers, recorders and processors — anything that incorporates YGDAI or mini YGDAI expansion ports.

The two cards are very similar in overall design and construction, and both offer conversion for eight channels of analogue audio, in the appropriate direction. The AP8AD is an input card, converting from analogue to digital, whereas the AP8DA is an output card providing digital to analogue conversion. In both cases the analogue interfacing is through a 25-pin D Sub connector, conforming with the ubiquitous Tascam wiring format, for eight channels of fully balanced line-level audio.

Apogee AP8AD/AP8DA £1291/£1056
  • Neat integration.
  • Reduced jitter in stand-alone systems.
  • Soft Limit function in A-D card.
  • Independently configurable levels.
  • Firmware doesn't yet support 88.2 or 96kHz conversion.
  • Not compatible with 01V.
  • If you upgrade to non-Yamaha gear, you'll also have to upgrade your converter hardware.
  • gh
When it comes to changing audio domains few companies do it better than Apogee. The AP8 cards provide an elegant way of incorporating eight channels of Apogee's high-quality conversion within almost any Yamaha YGDAI-equipped product.


Shrink To Fit

As unpacked from the box, these cards are formatted to fit a standard YGDAI slot, as found on the 02R or 03D consoles, for example. However, the mechanical design of the card is rather cunning and, with a little bravery on the part of the user, it can easily be modified (permanently) to fit a mini YGDAI slot, as found in later Yamaha products such as the AW4416 multitracker and SREV1 sampling reverb processor.

This engineering marvel is made possible by designing the card in two parts, linked by integral stabilising strips running the full length of each side. The front part carries virtually all the electronics and the metal interface plate. Halfway down the length of the card is a pair of mated connectors, and the remaining portion of card is really just an extension board, carrying only a few interfacing components to reformat the mini-YGDAI interface signals from the converters into standard YGDAI signals which are presented to the connector at the rear of the extension card.

If you require standard YGDAI interfacing, just plug the card into an appropriate slot in the Yamaha product of your choice. However, if you require a mini YGDAI interface, you have to carefully snap off the two edge runners which hold the entire assembly together, and then pull apart the central connector. Once the front metal interface has been replaced with a supplied alternative bracket, you are left with a fully functional mini YGDAI interface and a useless extender card.

With the power turned off on the Yamaha host, the card can be installed just like any other interface module, and when the host is powered up it recognises the presence of the appropriate card (some older Yamaha operating systems don't recognise the cards as being of Apogee design, but will work with them nonetheless). Unfortunately, though, the firmware in the 01V console is incompatible and cannot be used with the Apogee cards at all so, if in doubt, check first with your dealer. Apparently Yamaha are reluctant to upgrade the 01V software, since they feel it is unlikely anyone would want to install an option card which costs more than the console — fair point!

Ultra-low Jitter Clocking

The converters on both cards work at 24-bit resolution, unlike most other YGDAI and mini YGDAI converters, which provide only 20-bit conversion. However, the main reason to consider investing in these Apogee cards is because of the company's renowned Ultra-low Jitter Clocking. Jitter is a popular discussion topic among digital geeks and, to be fair, it is one aspect of digital systems where attention to detail pays sonic dividends. Essentially, jitter is the digital equivalent of wow and flutter on a tape recorder. It is minute timing variations in the precision of the sampling clock which cause quantisation errors in the sampling or reconstruction of analogue signals. Severe jitter can increase the noise floor well above the theoretical level of a 24-bit system, but even small amounts of jitter will compromise the depth and stability of stereo imaging, because the small timing variations disturb the localisation cues embedded within the stereo signal.

Clearly, then, if you wish to preserve the three-dimensionality and imaging precision of your stereo (or multi-channel) signal in the analogue domain it is crucial that jitter is removed from the clock signals employed in the A-D and D-A stages of a digital signal chain — and this is where Apogee score a big hit. Both the AP8AD and AP8DA are synchronised by the clocking signals provided by their Yamaha host, but the Apogee circuitry applies sophisticated and proprietary filtering and reclocking processes to ensure that, when these clock signals reach the A-D or D-A chips, they are as precise and stable as it is practical to achieve. That means that the A-D conversion captures the all-important phase relationships between concurrent signals precisely, and the D-A conversion reconstructs them with the same degree of precision.

 Dippy About Jumpers 
 Both cards can be customised for various operating levels via jumpers on the circuit boards. Further jumpers enable operation at doubled clock rates (88.2 and 96kHz), but the cards' firmware doesn't yet allow interface with Yamaha consoles at these rates — Apogee are currently working on sorting this out.

In the case of the AP8AD input card, a jumper is provided for each of the eight channels to set their maximum input levels to +24dBu, +18dBu (EBU standard), or +4dBV (for compatibility with nominal -10dBV semi-pro equipment). The AP8DA output card can be set for the same peak output levels, again with independent jumpers for each channel.

In addition, the AP8AD input card is equipped with eight dip switches accessible through the face plate. These switches activate or disable Apogee's 'Soft Limit' facility, which is designed to prevent accidental overloads. This is achieved by introducing a form of soft-knee limiting with a very fast attack-time to catch transients, emulating in many ways the saturation characteristics of an analogue recorder.


Listening Tests

So much for the science. The obvious question is: can you hear the difference? And the answer is... it depends! I installed the Apogee cards in an 03D mixer which I routinely clock externally from either an Apogee PSX100 converter or an Aardvark Aardsync master clock. Under these conditions, the Yamaha's own A-D and D-A converters perform very well — noticeably better than when the desk is running under its own internal clock. The difference is not 'Oh my God!' dramatic, but can clearly be observed with a decent monitoring system — stereo imaging is wider, deeper and far more natural.

After plugging the Apogee D-A card into the 03D's slot and configuring the desk to output a high-quality stereo digital source through both its own and the Apogee outputs, I have to be honest and say I heard little change. However, when I switched the desk to use its internal clock the width and depth of the Yamaha outputs closed down noticeably, whereas the Apogee outputs remained exactly the same. To test the A-D card, I took the analogue output from a high-end CD player (using material I had recorded myself) and split it to feed the Yamaha's own analogue line inputs plus two inputs on the AP8AD. The digital output from the desk was routed to my PSX100, so that the D-A side of the equation was independent and essentially isolated from any desk jitter. Once again, with the desk locked to the Aardsync master clock the difference between the two converters was negligible, but with the desk running on its internal clock the difference was marked — more so than when comparing the D-A card, in fact.

Yamaha make a lot of extremely good and highly cost-effective digital equipment. However, ultra-accurate and stable clocking is very expensive to manufacture, making it difficult to incorporate when the price margins are as slim as they are for products like the 01V, 03D and so on. For many users, the effects of such jitter as is present will be of little consequence, but high-end users will notice the benefits of the Ultra-low Jitter Clocking. In the majority of cases, people upgrade their systems with high-quality stand-alone converters — like my own PSX100, for example. However, these two Apogee cards provide a much neater solution in some ways, particularly in terms of their seamless integration.

infop.gif AP8AD A-D converter card, £1291.33; AP8DA D-A converter card, £1056.33. Prices include VAT.
Published December 2002