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CNR/AMR Audio Issues

More Than A SoundBlaster
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The introduction of CNR and AMR slots on the motherboard were supposed to help vendors lower costs and develop sound cards to use these slots, but so far very little has happened with regard to these slots. Battles among system makers and developers have not yielded a clear standard between the CNR and AMR technologies. Some motherboards have the CNR slot, while other motherboards continue to use the AMR slot, and still other motherboards do not offer either of these technologies. If this is confusing to you, you are not alone. If you need only basic sound, are not overly concerned about performance, and your motherboard happens to have one of these slots, this is an option, but finding a compatible card for your CNR/AMR slot could present a challenge.

One of the sound cards that use the CNR slot is Analog Devices' SoundMAX card, using Analog Devices' AD1885 coder/decoder (CODEC). The specifications for the SoundMAX using the CNR are: 1024-voice wave table, environmental reverb and multi-channel extensions supporting up to 6 channels of playback for 5.1 Dolby Digital, EAX and A3D. Recently, Guillemot announced a new collaboration with Analog Devices on the development and marketing of new CNR audio cards based on the SoundMAX technology. We will have to wait to see what this collaboration yields. But prior to moving to a sound card that supports the CNR or AMR technology, I think the first question to be considered is the following: "Will this move create another WinModem type CPU performance hit that I can afford?" Since CNR and AMR technology are not the focus of this article, we will save this discussion for another time. However, I wanted to include in this discussion what other sound card technology is currently available for CNR/AMR.

Cirrus Logic SoundFusion DSP

Sound card vendors got a big boost late last year when Cirrus Logic introduced the new CS4630 SoundFusion DSP. Turtle Beach chose the CS4630 DSP for use in its new Santa Cruz sound card. Guillemot, through their Hercules line, is using the CS4630 in the Game Theater XP. Guillemot is also using the Cirrus Logic CS4624 DSP in the Hercules branded Gamesurround Fortissimo II. Some motherboard vendors are using the SoundFusion DSPs for integrated audio on several motherboards.

The Cirrus Logic CS4630 SoundFusion DSP is an upgrade to the CS4624 PCI audio accelerator. With support for legacy compatibility modes, the CS4630 enables real mode DOS compatibility within PCI-only audio subsystems. This device, combined with application and driver software, provides a complete system solution for hardware acceleration of Microsoft's DirectSound, DirectSound3D, DirectInput, and Wavetable Synthesis. The CS4630 is based on the Cirrus Logic CrystalClear Stream Processor (SP) DSP core. The SP core is optimized for digital audio processing, and is powerful enough to handle complex signal processing tasks such as Sensaura 3D, 4-channel output, and hardware wavetable synthesis. The SP core, is supported by a bus mastering PCI 2.1 interface and a built-in dedicated DMA engine, with hardware scatter-gather support. These support functions ensure transfer of audio data streams to and from host-based memory buffers, providing maximum performance and minimal host CPU loading.

Most of the major features of the CS4630 are also found in the CS4624. The biggest difference between the CS4630 and the CS4624, from what I can understand, is that the CS4630 uses a 128-stream DMA interface and has 420 MIPs SLIMD DSP architecture with increased internal memory. The CS4624, on the other hand, uses a 96-stream DMA interface and has 300 MIPS SLIMD DSP architecture.

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