SoundStorm

SoundStorm was an advanced integrated 5.1 sound technology certification developed by Nvidia for the nForce2 platform based on the nForce audio processing unit (APU).

Certification

To achieve SoundStorm certification, a motherboard manufacturer had to include the nForce APU and include the necessary discrete outputs. It was also necessary to meet certain sound quality levels as tested by Dolby Digital sound labs.

The SoundStorm certification ensured that many manufacturers produced solutions with high quality sound output. For this reason, SoundStorm achieved significant popularity in the hardware enthusiast community, offering high quality for a bargain price. It was also, at the time, the only PC sound card capable of producing real Dolby Digital 5.1 output (a technology called Dolby Digital Live), which was important for home theater PCs.

Hardware

It is often referred to as an audio chip but this is a misconception. The audio 'chip' component of SoundStorm is the nForce APU, which is included in the MCP-D and MCP-T southbridges of the nForce and nForce2 chipsets respectively. A series of fixed-function and general-purpose processing units provide a combined total of reportedly 4 billion operations per second. A fully programmable, Motorola 56300-based digital signal processing is provided for effects processing but with very limited support under DirectX on the PC. The DSP on the APU was normally driven by code largely derived from the 3D audio middleware company Sensaura. The Sensaura middleware was also used by the Windows drivers of nearly every sound card and audio codec other than those by Creative. Unlike the usual software implementations of the Sensaura code, the SoundStorm solution ran the same code on a hardware DSP, which resulted in extremely low CPU usage. It was also capable of realtime Dolby Digital 5.1 encoding. Compared to other audio solutions of the day, the difference in CPU usage when running popular multimedia applications was as much as 10-20%. While the Creative Audigy offers similar performance, it does so at a much higher price point, and only as a discrete add-in solution.

Drivers

Since the SoundStorm solution was a general-purpose DSP where code was uploaded to the card by the device drivers at boot time, this made it easy to add new functionality to the card. However, it also meant that it was not possible to create third-party device drivers for the SoundStorm, since they did not have access to the DSP code. Linux drivers for the SoundStorm actually talk directly to the audio codec (like a RealTek ALC650), bypassing the APU completely and doing all audio operations in software.

It should be noted that the nForce2 APU was a purely digital component, and that motherboard manufacturers still had to use codec chips such as the 650 from Realtek for the audio output functions, including the necessary digital to analog conversion (DAC). After the demise of SoundStorm, codec chips such as the Realtek 850 have become standard integrated audio solutions, with audio processing functions offloaded on the host processor. As such, the quality of the device drivers is very important to ensure reasonably low host processor usage, without audio quality issues.

Xbox

SoundStorm development was originally funded by Microsoft for use in the Xbox gaming console. At time of writing reportedly a second generation chip has been developed, this time with funding from Sony, as part of the PlayStation 3 project. It is hinted SoundStorm may make return to the PC scene, possibly as part of a multimedia graphics card, along the lines of the original NV1 card, rather than as a discrete or onboard solution. While there did appear to be plans for a discrete product at one point, this never materialised.

Discontinued

Nvidia decided the cost of manufacturing SoundStorm as an integrated product was too high, and while it was retained on nForce2 Athlon XP boards, nForce3 and beyond dropped it.

Furthermore, in the absence of a formal certification process, there is little incentive for motherboard manufacturers to use the quality of components necessary for high fidelity output. It needs be considered that from a purely technical point of view, there is no reason why onboard sound from motherboards without the nForce APU and SoundStorm certification cannot reproduce non-processed sound such as an MP3 or CD without effects applied, as well as can a SoundStorm certified nForce2 motherboard.

Alternatives

Other manufacturers have since produced stand-alone sound cards based on C-Media chips such as the CMI8788 which also provide Dolby Digital and DTS encoding features. These manufacturers include Turtle Beach and Auzentech. A software alternative is redocneXk, which provides real-time AC3 encoding comparable to SoundStorm on Creative's Audigy2 and later sound cards. However, early versions of these alternatives may still be lagging behind the SoundStorm in terms of reliability, ease of use, and CPU usage.

Driver Support For Linux Systems

To use the AC3 encoding on SPDIF under Linux, a binary driver provided by Nvidia is required. Starting with kernel 2.6.16, Nvidia's driver package will fail to build, but a workaround is available at the Ubuntu forums: http://www.ubuntuforums.org/showthread.php?t=253725

To output to SPDIF without AC3 encoding, the intel8x0 driver can be used by enabling the dmix capabilities of ALSA.

Example /etc/asound.conf:

pcm.nforce-hw {
   type hw
   card 0
}
pcm.!default {
   type plug
   slave.pcm "nforce"
}
pcm.nforce {
   type dmix
   ipc_key 1234
   slave {
       pcm "hw:0,2"
       period_time 0
       period_size 1024
       buffer_size 32768
}
}
ctl.nforce-hw {
   type hw
   card 0
}