Using the X-Fi Elite Pro Auxiliary Input

The Creative Technologies X-Fi Elite Pro sound card has several different line-in connections available. The best overall performance (S/N) performance is obtained using the Line-In jack on the PCI sound card (the multifunctional 1/8" stereo FlexiJack connection), while somewhat lower performance is obtained using any of the line-in jacks on the external I/O console. This performance difference is due to the different A/D converters used for the main sound-card line-in and the line-ins of the external I/O console.

While typically not used, the main sound card has an Aux In analog 4-pin jack which can be used for an analog connection to a CD drive. This Aux In connection can be enabled with the Creative Audio Creation Mode Console (ACMC) mixer panel (Line-In, Auxiliary, Microphone choices) and uses the same high performance A/D converter as the main Line-In connection.

It is easy to configure external access to the Aux In connector using a standard analog 4-pin shielded CD cable and a small box. Multiple types of stereo jacks could be set up as a daisy-chain connect, providing convenient access for different types of audio analog connection cables although only one type of connection should be used at a time. Since the Line-In/Aux In can be quickly switched in the ACMC, this provides a convenient way of having multiple switchable access to the low-noise input configuration without having to manually change cable connections for different sources.

The images below show a simple implementation, using a short CD cable wired to stereo RCA jacks in a small shielded box of dimensions 1.5" x 2" x 2.5":

The Red/White cable is the Right/Left Channel. While only one of the two center pins in the plug is used, both center pins in the jack are connected to the common ground.

The RMAA noise spectra below, with no connection to the main Line-In jack or to the externally-routed Aux In show that the Aux In has somewhat lower noise. The configuration settings were Record-In level set at 50% (0 dB), 96 kHz sampling rate in both RMAA and ACMC and all playback inputs muted and no effects/EAX enabled. The connection for monitoring was selected in the Recorder source selection in the ACMC window. The actual noise floor achievable and differences between the main Line-In and Aux In will probably depend to some extent on the quality of the PC power-supply and exact physical layout and shielding inside the desktop. For comparison purposes, the noise spectrum of the Auxiliary 2 Input on the back of the external I/O console is shown, showing poorer noise background:

The Aux In noise spectrum with connected external home-made break-out box but with no input connection.

The main Line-In noise noise spectrum with no input connection.

The external I/O console Auxiliary 2 noise spectrum with no input connection.

Integrated RMS noise measurements for the 96 kHz sampling rate (noise bandwidth ~ 45 kHz) for the three above connections are:
    Aux In:    7 uV 

Line In: 14 uV

Aux2 In: 18 uV

A comparison of the Line In and Aux In connection performance using an RMAA "loop back" test (from the Stereo Line-Out to either input) shows only a slight improvement in noise with the Aux In connection. This is due to the limitation of the X-Fi Elite Pro line-out noise background level.