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Old 15th December 2010, 01:23 AM   #11
Pano is online now Pano  United States
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Thanks very much to Paul, Murphy and all who participated in this test. I read the posting over at RedSpade. As a potential miniDSP customer, this sort of thing is great to read.

Some thoughts and ideas of my own, FWIW, IMO, YMMV, etc.

The reason the miniDSP seems to have more treble or more air even when the FR plot says no, may be because of greater distortion - harmonic and inharmonic - and phase problems at the top end. That can sound like more top end even if it does not show on the FR plot. Don't know if that is the case, but it's worth a look.

The DCX. If it's clipping on a digital input and your inputs and EQ are set to 0dB, then it's the digital signal that is clipping. Have a close look at what is upstream. DEQ, playback software, or the sound file itself. There are plenty out there that are badly clipped. I see them flash the red lights on my DCX, too. Many software players also have digital gain and replay gain leveling. Check those.

I can post a couple of test tones if you want to double check this. it is not related to the 110 ohm termination. Going to 75 ohms is fine, but won't change the clipping - unless there is something really odd going on.

Murphy. Why do you say that you found it good to keep away from digital attenuation? Can you explain further?

Thanks guys.
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Old 15th December 2010, 04:31 AM   #12
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Did you guys get to compare the DSP's to the passive Marchand, i believe it was mentioned , but i could not find it...
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Old 15th December 2010, 04:52 AM   #13
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Originally Posted by panomaniac View Post
Murphy. Why do you say that you found it good to keep away from digital attenuation? Can you explain further
Hi Panomaniac,

Well, where do I start..

The only conclusive reults we got between DSP's was that whenever you attenuate the signal (move below 0dB) using the DSP controls, the sound quality is reduced to the point where it's easily noticable in our "instant switching" listening tests..

Sound becomes grainy and quite noisy, Loss of dynamic range, reduced frequency response, loss of detail in the sound.. Etc..

It's like listening to a song that's been compressed using the lowest bit rate possible!! This is not surprising as these DSP's use 'bit stripping' for signal attenuation, so in affect, you are compressing the signal..

For our second listening test, one of the guys wired in an analog pot for level control, that way he could leave the attenuation on his MiniDSP at 0dB, and it worked a treat!!

The stock DCX and MiniDSP both suffered the same result when using digital attanuation. (Modded DCX uses analog volume control)

Hope this helps..

Murphy
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Old 15th December 2010, 04:55 AM   #14
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Did you guys get to compare the DSP's to the passive Marchand, i believe it was mentioned , but i could not find it...
Hi Wayne,

No, the owner of the DEQX, who now owns a Marchand did not have it available at the time of out listening test.. But I believe it's on the cards for our next GTG :-)

Cheers..
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Old 15th December 2010, 06:29 AM   #15
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Originally Posted by MurphyUHF10 View Post
Hi Panomaniac,
For our second listening test, one of the guys wired in an analog pot for level control, that way he could leave the attenuation on his MiniDSP at 0dB, and it worked a treat!!

The stock DCX and MiniDSP both suffered the same result when using digital attanuation. (Modded DCX uses analog volume control)
Can I assume that the pot for the miniDSP was post DAC?
I wonder about a hybrid system for active crossover attenuation, where most of the attenuation is done post DAC via analog pots, but the day-to-day volume control is done in the digital domain.

Was the DCX analog volume control using PGA chips?
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Old 15th December 2010, 12:25 PM   #16
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Thanks Murphy, that helps.

I've never heard a problem with digital volume at 20 bits or above, but have not heard the miniDSP.
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Old 15th December 2010, 01:26 PM   #17
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We didn't do the test blind. While this may disappoint some, but I felt that using instant switching would be revealing enough. We did this test for our own curiosity, but no one had a point to prove. In a previous informal comparison, I found that was enough even with levels obviously not matched. No one in that test could hear a difference with the digital conversions vs a loop through wire, not even one person there who was certain a difference would be heard.
In other words this is not a valid test. It is just a whole lot of subjective opinions from people who may or may not have a preconceived bias. I'd hardly call that conclusive

Also every CD ever sold comes with built in quantisation errors due to the finite resolution of the binary number system and there is nothing you can do about it no matter how good you think your analog reproduction system is !!

regards
trevor

Last edited by Trevor White; 15th December 2010 at 01:29 PM.
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Old 15th December 2010, 10:49 PM   #18
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Can I assume that the pot for the miniDSP was post DAC?
I wonder about a hybrid system for active crossover attenuation, where most of the attenuation is done post DAC via analog pots, but the day-to-day volume control is done in the digital domain.

Was the DCX analog volume control using PGA chips?
Hmmm, I don't actually know if the pot was pre or post DAC.. I will check with Gainphile,, but I'd say to keep s/n ratio good, the pot would have been post DAC..

The analog volume control in the modified DCX is a CS3318..

Cheers..
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Old 15th December 2010, 10:53 PM   #19
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Originally Posted by Trevor White View Post
In other words this is not a valid test. It is just a whole lot of subjective opinions from people who may or may not have a preconceived bias. I'd hardly call that conclusive

Also every CD ever sold comes with built in quantisation errors due to the finite resolution of the binary number system and there is nothing you can do about it no matter how good you think your analog reproduction system is !!

regards
trevor
Hi Tevor,

Yes, we did do blind tests.. Literally,, the "switching person" was behind a curtain with a big pillow over the switch box.. That way you couldn't hear the click of the switch, AND, you couldn't see his arms moving while switching.. I'd definately say it was a blind test :-)

But really, blind or not blind, "instant switching" is a fantastic aid for this sort of stuff..

Cheers,
Murphy
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Old 15th December 2010, 11:15 PM   #20
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right, see this is where systems like the sabre's integrated digital volume are a different ballgame, the attenuation is done in the dac registers themselves. I use this for my 2 channel rigs with overwhelming superiority to analogue to my ears and shortly the 8 channel ackodac will allow this sort of system for crossovers. this is where i'm headed also adjusting the gain in the spdif stream itself pre-dac is transparent with something like an RME9652
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