Krell Foundation Surround Processor Test Bench

Test Bench


The above chart shows the frequency response at the preamp outputs of the Dolby Digital decoder. Left (aqua): –0.00 dB @ 20 Hz, –0.17 dB @ 20 kHz. Center (green): +0.01 dB @ 20 Hz, –0.19 dB @ 20 kHz. Left surround (red): –0.00 dB @ 20 Hz, –0.31 dB @ 20 kHz. LFE (purple): Normalized to the level @ 40 Hz: +0.02 dB @ 20 Hz, upper –3 dB @ 118 Hz, upper –6 dB @ 121 Hz.

Analog frequency response in Preamp mode:
–0.05 dB @ 10 Hz
–0.01 dB @ 20 Hz
–0.00 dB @ 20 kHz
–0.03 dB @ 50 kHz

Analog frequency response with signal processing:
–0.66 dB @ 10 Hz
–0.19 dB @ 20 Hz
–0.13 dB @ 20 kHz
–58.61 dB @ 50 kHz

There was no multichannel input to measure. The analog THD+N was less than 0.009% at 1 kHz with a 100-millivolt input and the volume control set to 106. Crosstalk with a 100-mV input was –100.61 dB left to right and –99.44 dB right to left. The signal-to-noise ratio with “A” weighting was –128.33 dBrA.—MJP


Video: The Krell performs no upconversion but only does a direct HDMI video passthrough. However, in doing so, we first discovered it was clipping any information that sits below video black or above video white, information that may be encoded in the footroom and headroom provided in the digital video standard. Clipping below black makes it more difficult to set the Brightness (black level) control. Clipping above white is more serious, as it can crush the extreme whites (such as detail in brightly lit snow or clouds, depending on how the source has been transferred). Krell responded with a series of firmware updates that we confirmed had fully corrected the issue for both YCbCr and RGB signal types and allowed us to issue a perfect score for video. Users in the field should be sure to update their firmware to version V1.15 Jan 16, 2014 or later for optimal video performance.—TJN

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