原来我以为只有 E-WDM 驱动才可以这样，现在搞清楚了，只要有 WDM 驱动，使用 Sonar 也可以获得原来只有 Cubase 在 asio 下的极小延迟。
Electronic Musician 杂志中有关于 Sonar 在 WDM 驱动下的文字，里面用 Live 声卡在不同驱动下的表现作了一个测试，在奔三700 / Windows 98 SE 下，使用 MME 驱动的 44.1 kHz stereo 的延迟是 187.5 ms ，使用 WDM 驱动的 44.1 kHz stereo 的延迟是 10 ms （相当于 96kHz 情况下的 2 - 3 ms ）：
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WDM DRIVERS
Sonar offers some significant under-the-hood enhancements, including support for Microsoft's new WDM technology. If your sound card offers WDM audio drivers, you can achieve extremely low latency, which lets you use real-time effects when monitoring live input. WDM also improves performance when you play software synths from an external controller.
Sonar still supports the older Windows Multimedia Extensions (MME) audio drivers for compatibility, but the WDM drivers clearly make a difference. I tested the MME and WDM drivers for the Sound Blaster Live card on my Pentium III/700 MHz PC running Windows 98 SE. The results were quite astonishing. Like Pro Audio 9, Sonar lets you adjust for latency using the Mixing Latency parameters in the Audio Options dialog box. With the MME drivers installed, the lowest buffer size I could achieve was 62.5 ms, resulting in an effective latency of 187.5 ms for 44.1 kHz stereo audio. With the WDM drivers installed, the buffer size and effective latency were reduced to 10 ms. Amazing!
As with all new technology, however, there are some caveats. WDM drivers are supported only under Windows 2000, Windows ME, and Windows 98 SE. If you're running Windows NT, you're out of luck; Sonar won't even install under Windows NT. Sound-card manufacturers are still playing catch-up too, so don't be surprised if you find that WDM drivers are not yet available for your hardware. Fortunately, the vast majority of Sonar's features work fine without WDM drivers. You'll just miss out on optimal input monitoring and live performance of software-based instruments.