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  Analog Devices' SoundMAX 3.0 with SPX 
  May 30, 2001, 09:00am EDT 

AC'97, Too Cheap For Its Own Good?

By: Dan Mepham

In 1996, the Audio CODEC ’97 standard was introduced. The premise on which AC’97 is based is similar to that of a software modem, namely that some of the work performed by expensive hardware could be offloaded onto the host CPU through the use of specially designed drivers.

As CPU speeds began to push past the 500 MHz barrier, it came to be that in most cases, most PCs had an over-abundance of CPU horsepower that wasn’t being put to good use. At the same time, there was an expensive DSP (digital signal processor) on the PC’s soundcard that was idle as well. It was very rare that even one of those processors was being used to its full potential, let alone both of them at the same time. (remember, we’re talking about average computer users here – in most homes/offices, the actual workload placed on a system is very light) If one was looking to reduce the cost of a PC, that mostly-unused DSP on the sound card might be a good place to start.

And that’s precisely where AC’97 comes in. Through use of special purpose drivers, the host processor could be made responsible for audio processing as well, thereby eliminating the need for an external daughter-board. The biggest advantage is obviously cost, however there are other advantages such as ease of integration and support. At the same time, there are disadvantages, such as upgradability and performance, which we’ll get into later.

The standard AC’97 audio could be supplemented with a 3rd party audio controller as well, to improve quality, performance, or both. Unfortunately for AC’97, in order to prevent the load on the host CPU from being noticeable, and in order to keep costs down, the technology was somewhat limited in most implementations. Most AC’97 systems support, at best, two channels and lower sampling rates, and suffered from poor S/N ratios, and in general, a lack of features common to most any PCI sound cards.

1. Introduction
2. AC'97, Too Cheap For Its Own Good?
3. SoundMAX, Taking AC'97 a Step Further
4. The Latest SoundMAX, SoundMAX 3.0 with SPX
5. CNR Makes an Appearance
6. Test Setup & Procedure
7. Test Results
8. Sound Quality
9. Conclusions

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