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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it. |
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In Reply to: Re: Perpetual P1A's Resolution Enhancement Alogrithm posted by FMS on August 30, 2001 at 07:52:32:
Most DAC algorithms are varying implementations of "sinc" function convolution. (Convolution is a mathematical method of determining the ideal interpolation values between samples, using the amplitudes of *adjacent* samples multiplied by the filter function centered at the nearest sample. These values are then added to determine the interpolation value.) The differences are mainly how accurately the convolution is implemented and executed, the size of the "window" containing the "sinc" function to be convolved with the signal, and the resolution (fineness of the upsampling/oversampling) of the convolution.A few DACs use algorithms that convolve the digital signal with a different function. Wadia, for example, uses a patented "spline" function, which has poorer frequency response (less like a near-ideal brickwall), but superior time response (the "spline" function has a sharper attack and decay => less "time smear" than the "sinc" function).
The Perpetual white paper did not mention the function the algorithm used, so it's most-likely the "sinc" function. Although we cannot rule out the possibility of a "proprietary" filter function.
The misleading portion of the white paper implies that interpolation was a **brand-new** innovation by Perpetual, using false information of how other DACs' digital filters worked. (Oversampling using "bogus" values, instead of interpolated ones.) The paper uses this false information to give the impression, to those not familiar with digital processing, that interpolation was a brand-new implementation of digital filtering (and relating this "breakthrough" with "resolution enhancement"), where in reality, interpolation has been both a long-established and the **predominant** filter methodology.
The change in sound between DACs is from the refinement and *execution* of the algorithm. Since there are variations on how filter algorithms are executed, the DACs sound different. Complicating matters is the fact the digital signal received by the DACs also varies as a function of transport and digital cable. One DAC may sound better with a certain transport and/or cable, where another DAC may sound better with a different transport and/or cable. The key is finding a satisfying combination, which can be exasperating, time-consuming, and expensive.
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Follow Ups
- Re: Perpetual P1A's Resolution Enhancement Alogrithm - Todd Krieger 00:43:17 08/31/01 (1)
- Very excellent post Todd! (nt) - steve b 16:07:40 09/01/01 (0)
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