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Sound Card Performance Technical Benchmarks

TechTalk

SNR & THD+N

PCAVTech large-signal SNR measurements include modulation noise. SNR measurements often used in the industry, made with little or no signal present, fail to include modulation noise.

For example, one of the finest cards tested, the LynxONE, shows loopback dynamic range measurement (made with a - 60 dB FS signal present) shows a noise floor from 3 to 6 dB lower than that seen for any of the tests made with a FS signal present. PCAVTech believes that this 3 to 6 dB increase is due to, admittedly trivial amounts of, modulation noise in the LynxONE.

PCAVTech believes that since sound cards are used with large signals present, noise should be measured with large signals present. In some cards, such as those based on the very common HT 1869/CMI 8330 chipset, PCAVTech has found spreads as large as 40 dB between SNR and dynamic range. For the HT1869/CMI8330, large signal SNR is about 30 dB, indicating that modulation noise might be the most noticable form of noise it has. While this is an extreme example, other less extreme, but still significant examples exist. One is the Sound Blaster Gold; a card that has been recommended widely for use in professional audio, in the past. On the other hand, the spread between SNR and dynamic range for the LynxONE is relatively small, and mostly explained by the noise analysis THD issue mentioned in the previous paragraph.

In the case of the LynxONE; this is a very abstract argument, because of its high performance. Audible noise is not normally going to be an issue with the LynxONE! However, PCAVTech often measures equipment with far lower performance, where modulation noise might exist at audible levels. To maintain consistancy across all its reports, PCAVTech measures LynxONE SNR using procedures that measure modulation noise along with any other noise sources present.

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