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Discussion Starter #1
I have been struggling with the digital output from my Sherbourn P-7010A Preamp/Processor, which appears to be imposing a de-emphasis filter of some kind on my source. This happens regardless of whether the source is digital in, or analog (the Sherbourn has a nice A/D for analog sources, providing a 48KHz sampled digital out).

While the effect is easily audible on recorded material from the digital out, I have quantified the problem by recording with a Sony PCM-D50 flash recorder, for example, which creates a wav file from the spdif optical stream. Using white noise, the recorded file can be analyzed with Audacity, for example, where the power spectrum then displays a "shelf filter" with a -3dB roll off around 3.5kHz or so, and then plateaus at about -9.5dB or so around 13-15KHz, where it stays out past 20KHz.

This filtering appears to be similar to what was once used (sparingly) in the early days of CD's as a pre-emphasis/de-emphasis pair to overcome fledgling electronics at the time, but I can think of no reason why it would be imposed by the pre-pro. Sony assures me the flash recorder has no de-emphasis filter, so even if for some reason the pre-pro tripped the flag bit in the spdif standard for de-emphasis, it should not happen in the file. It also seems to have some similarity to curves I have seen associated with DolbyB.

I have tried setting the source input options for sources to be conventional stereo, pro-logic II, etc., but this seems to have no impact.

My work-around is to apply my best effort at the inverse filter using Sony SoundForge 9 and a very nice parametric equalizer directX plug-in available from the web. This, however, is tedious and I'd much rather get to the root of the problem.

If anyone has any ideas as to what's causing this, I would love to know!

Best Wishes,

Tom
 

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Anything your Pre-pro is doing that is that drastic should either be documented in the manual (and defeatable) or is a significant design flaw. Take a good read of your manual (likely available online if you've lost your original) and let us know what you find.
 

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Discussion Starter #3
Thanks, eugovector, for the reply.

I've been on this problem for a bit of time, and have certainly gone into some depth with not only the manual, but checking and experimenting with relevant feature settings. As noted in my post, they seem to have no impact, and nothing remotely resembling any options that would have symptoms of this nature is noted in the manual.

I'm quite reluctant to represent this as a design flaw, because it could be due to some issue or compatibility problem that I am simply unaware of, and hence my request to the user community in case anyone has any ideas.

I've also been in touch with the vendor. They don't seem to be aware of any such issue, but had not conducted any tests to try to replicate my problem either. The unit (Sherbourn PT-7010A) is purported by several audiophile maganize reviews & sites to share a design core that is the same as one of the Sunfire and Emotiva units, I believe, and I had hoped that maybe someone had seen something like this before.

In the end, it could of course also be a failed chip for the digital out function. However, the fidelity is excellent once I apply the inverse filter, so it seems that would be a rather strange digital failure to produce this outcome. It is precisely for this reason that I thought someone expert in digital audio might know what the likely culprit is.

So -- again, if anyone has seen something like this crop up before, I'd be eager to learn about it.

Best Wishes,

Tom
 
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