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Gryphon Diablo 300

To S. Andrea Sundaram,

I have read your article on digital vs. analog volume controls ("What’s Wrong with Digital Volume Controls?") and was wondering if you could you say something about hypersonic effect, or ultrasound-quantization noise that affects the digital system and how it affects digital and analog volume controls.

One of the reasons I never replaced my old 5.1-input analog receiver is its analog volume control, as it gives far better and smoother sound, especially at low volumes when compared to later models using a digital volume control. I have not managed to find any later-model multichannel receivers using analog volume controls. If you know of any, they would be interesting to know about, as that feature only seems to be found on two-channel amplifiers.

Thanks and best regards,
Robert

I see a few different questions here, and I'll try to answer each. The bandwidth of a digital volume control is limited to half of its sample rate -- e.g., a volume control that operates at 192kHz will not pass signals above 96kHz -- whereas the bandwidth of an analog volume control is practically infinite. That said, if your music is coming from a digital source (CD, DVD, Blu-Ray, or computer file), then it already has a strictly defined upper-frequency limit and a digital volume control operating at a sample rate as high or higher than the source will not restrict the music's frequency response. Almost all DACs have a low-pass filter on their outputs to remove the out-of-band noise that results from playing back a quantized signal; that filter is what allows them to reproduce smooth sine waves rather than stair steps. A carefully designed and built analog volume control will outperform a digital one, but the differences are generally quite small.

If the signal entering a home-theater receiver is digital, then there is little reason to eschew a digital volume control. If, on the other hand, you are connecting an analog signal, you would want to avoid additional A/D and D/A conversions by using a receiver's "source direct," or similarly named, mode. Though almost all home-theater receivers display the volume digitally, that doesn't mean that they're using digital volume controls; they are often digitally controlled analog circuits. The mass-market brands rarely state what technology they are using. Audiophile companies -- like NAD, Cambridge Audio, and Anthem -- on the other hand, are likely to list digital volume control as a feature. A knowledgeable dealer can also be of help. In the end, there are many factors affecting a component's sound, and your ears will be the best arbiters of quality. . . . S. Andrea Sundaram