Audio examination
The Realtek ALC650 features on a number of motherboards today. Motherboard designers are keen to exploit its price-to-performance ratio. The Southbridge passes on the audio signal to the CODEC, and it decodes and routes the sound you hear from your speakers. With a SNR (signal-to-noise ratio) of greater than 90dB, it's better than the majority of on-board CODECs. The CODEC can output to 18-bit accuracy. That's better than the native 16-bit for CD-based audio. A higher bit accuracy offers a closer representation of the original sound. Further, the CODEC has the ability to output to digital audio to compliant receivers via a 20-bit S/PDIF (Sony / Philips Digital Interface) output, either in coaxial (RCA) or fibre (optical) form. Optical is regarded as having the better sound quality. With the ALC650, the S/PDIF functions are usually carried out by an add-on bracket hosting the digital outputs. A 6-speaker setup can be enabled via the Realtek control panel.
The audio driver bundled with the Shuttle is shown above. The Intel ICH4 SB offloads the audio to the AC'97 2.2 ALC650 CODEC. After this, the onus is on the CODEC to route the sound.
Notice how the line-out jack doubles-up as the rear speaker outlet when selected from the control panel. This is how we approach 6-speaker sound from only three audio jacks. They're multi-purpose.
The microphone jack is substituted to provide the the additional center / subwoofer connections.
It's not going to rival dedicated, discrete sound cards in overall quality, but it does feature some effects of its own. Children love to play with the environmental settings.
A fair degree of user manipulation is afforded by the associated software package. That's why a number of OEMs love the premium on-board sound CODECs. They add very little to overall motherboard price, but do add to the systems' features list. If playing MP3s and watching movies is your main audio requirement, give the on-board sound a chance before you splash out on a dedicated card. The distinction between budget, dedicated cards and on-board sound will be blurred further when Realtek, and others, begin shipping AC'97 2.3-compliant CODECs. The ALC655/658 will feature intelligent jack-sensing technology, an upgraded S/N ratio, and even greater audio manipulation.
To show you just what kind of performance degradation we suffer when using sound in gaming, the following graph shows the performance of the AB48PN with no sound, 2-channel, 4-channel, and 6-channel sound. Formal benchmarks are always carried out with sound disabled, but we all play games with sound; often with advanced EAX or positional audio.
~100FPS is taken away from our best benchmark score. Just remember this when comparing boards' performances.
