Jun 27, 2005 at 7:46 PM
- Apr 17, 2005
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- Apr 17, 2005
The X-Fi sample rate converters use a unique three-stage architecture, as illustrated in figure 4. The first stage precisely doubles the original sample rate in a particularly computationally efficient manner. The second stage uses a poly-phase FIR filter to produce a sample rate that is four times the desired final output sample rate. The third and last stage reduces the sample rate by a factor of four to produce the desired sample rate. As with the first stage, this process is particularly computationally efficient.
The first stage doubles the original sample rate to provide a new signal at a sample rate of 88.2 kHz. The poly-phase FIR second stage converts this signal to a sample rate of 192 kHz by operating at a sample rate conversion ratio of two times 48/44.1. The final stage reduces the sample rate to the desired output rate of 48 kHz.
The expressed goal of the X-Fi sample rate converters is to provide audio quality limited only by the inherent analog noise of the analog-to-digital converters, while using many series and parallel sample rate converters.
The measured THD+N performance of X-Fi converting 44.1 kHz to 48 kHz is shown in figure 6. A full level sine wave at nearly any frequency produces distortion below -136dB (as measured by an Audio Precision distortion analyzer). The pass band ripple for this example is ±0.00025dB.
The X-Fi sample rate converter supports a wide range of pitch shifts from zero to three octaves. The flexible audio routing of the X-Fi architecture means that audio can be taken through two sample rate converters in series to extend the pitch shift range even more.
Even with the advanced X-Fi hybrid SRC architecture this quality level doesn't come easy. The special purpose sample rate converter engine in X-Fi performs over 7 billion arithmetic operations per second.
Based on a novel architecture, the Creative X-Fi sample rate converters provide unprecedented audio fidelity, producing highly accurate 3D virtual environments and flawless synthesized music. Because of their extremely low ripple and exceptional THD+N performance, they form transparent digital patch cords, eliminating the headaches of sample rate synchronization. The Creative X-Fi audio processor provides flexible signal routing and the capability to operate at different sample rates to allow "bit-accurate" recordings when possible. When sample rate conversion is needed the user can simply listen to and record audio in an intuitive and creative way, thereby embracing the benefits of sample rate conversion and simultaneously enjoying phenomenal sound quality!