alexwgoody Posted July 16, 2013 Share Posted July 16, 2013 I am wondering if anyone can speak to or link me to any information regarding the harm caused by multiple A/D to D/A conversions (assuming relatively high-grade components). I am imagining using up to 3 conversions (does more matter?). I ask because I run multiple types of listening formats- both digital and analog, 2 channel & multi-channel currently all in multiple rigs- and have found success in my current DSP use in my two-channel all digital computer audio system (primarily in DRC from REW & digital crossovers on my speakers/subs). I've seen very little useful information with basic Google searches and would love to read some information/graphs/papers. I am no engineer, but have done my best to become knowledgeable and am able to understand some of the math, interpret graphs and understand the research. I have multiple reasons for wanting to know the possibly harmful effects to see if it is worthwhile to use all of my sources in my digital rig and am interested in running a surround processor (and turntable) into my miniDSP 10 x 10 to be able to run multi-channel surrounds with my current digitally crossed-over room corrected speakers and subs (2). Thank you. (I would just try it on my own and listen- but I do not want to spend any more money/time than is necessary. Living on a relatively tight budget, buying new gear - especially the surround processor just to be disappointed with the sound quality would devastate my bank account) Link to comment
alexwgoody Posted July 16, 2013 Author Share Posted July 16, 2013 FYI- I also posted this thread to AVS Forum and received this link as an answer: Converter Loop-Back Tests Link to comment
dan92075 Posted July 17, 2013 Share Posted July 17, 2013 I use a Wisdom SC-1 A good sign is that I can hear the difference in my upstream components: upgrading my DAC, power cable to my DAC, even the USB cable to the DAC I can hear an audible difference In contrast, when I had my Denon AVp-A1 preamp in the chain it was obscuring things and much harder to hear differences In fact, I do not understand why the SC-1 is NOT limiting the sound After all its just another DAC at the end of the day And its an older technology, 24-bit and not as good my newer Wyred Dac2se Perhaps because its being fed by the ADC and maybe jitter is not an issue? Link to comment
alexwgoody Posted July 17, 2013 Author Share Posted July 17, 2013 I'm not sure I understand. Do you mean that running analog multichannel from the Denon vs. usb from your computer into the Wisdom SC-1 is actually making a negative SQ difference due to the extra A/D conversion and this amount of degradation is equivalent to "losing" the cable upgrade? (I assume you are comparing the same recordings and had no volume attenuation/DSP before the SC-1) You then said that the SC-1 is NOT limiting the sound. unless I am misreading this, you are saying here that the A/D conversion is not making a difference versus a digital feed. I am confused.... Link to comment
schawo Posted July 17, 2013 Share Posted July 17, 2013 I am wondering if anyone can speak to or link me to any information regarding the harm caused by multiple A/D to D/A conversions (assuming relatively high-grade components). I am imagining using up to 3 conversions (does more matter?). I have absolutely no clue, what are you talking about. What do you mean multiple conversions. Can you describe your setup? I've done some loopback tests before. I can send you some audio files for abx testing, if you are interested. http://www.premiermixing.com SqueezeBox Touch / MacBook Pro -> Audirvana Plus -> Firewire -> Mytek Stereo192-DSD -> GAC1 Pro -> Luxman L-410 -> Rubicon RP63F SqueezeBox Touch / MacBook Pro -> Audirvana Plus -> Firewire -> Mytek Stereo192-DSD -> GAC1 Pro -> DIY Headphone Amp -> Beyerdynamic T70 / AKG K500 / Sennheiser HD540 / Shure SRH840 Mac Pro -> Audirvana Plus -> Lynx AES16 -> Lynx CBL-AES1605 -> Lynx Aurora -> Mogami 2932 XLR -> M-Audio EX66 Link to comment
dan92075 Posted July 17, 2013 Share Posted July 17, 2013 I'm not sure I understand. Do you mean that running analog multichannel from the Denon vs. usb from your computer into the Wisdom SC-1 is actually making a negative SQ difference due to the extra A/D conversion and this amount of degradation is equivalent to "losing" the cable upgrade? (I assume you are comparing the same recordings and had no volume attenuation/DSP before the SC-1) You then said that the SC-1 is NOT limiting the sound. unless I am misreading this, you are saying here that the A/D conversion is not making a difference versus a digital feed. I am confused.... Sorry - let me clarify by showing configurations: All tests are done in stereo mode only 1) Touch -> stock USB -> Wyred Dac2se -> Denon AVP-A1 digital AD/DAC mode -> Wisdom SC-1 -> Merrill Amp -> Wisdom L75 2) Touch -> stock USB -> Wyred Dac2se -> Denon AVP-A1 in analog bypass -> Wisdom SC-1 -> Merrill Amp -> Wisdom L75 3) Touch -> stock USB -> Wyred Dac2se -> Wisdom SC-1 -> Merrill Amp -> Wisdom L75 4) Touch -> Wireworld Platinum USB -> Wyred Dac2se -> Wisdom SC-1 -> Merrill Amp -> Wisdom L75 So very little difference between 1) and 2) -> this implies that the A/D to DAC conversion of Denon is transparent Between 2) and 3) a big step up -> this implies that the primary limiting factor was the preamp of the Denon Between 3) and 4) another step up -> this implies that USB cable was limiting factor I should also say that the upgrade from Wyred Dac2 to Dac2se was a major step up in sound - as others are reporting So the point here is is that the Denon preamp, the cables, etc are all noticeably apparent - so the SC-1 is not the one limiting the pipe. Its also interesting the difference between 1) and 2) show no noticeable difference so that ADC to DAC stage did not make a difference either. So that brings up an interesting point - why are ADC to DAC stages transparent, yet I need to spend so much money on the original DAC by itself to get good sound? Something I don't fully understand. . . maybe because the ADC and DAC are contained within the same box - and jitter and noise are easier to control? Link to comment
schawo Posted July 17, 2013 Share Posted July 17, 2013 They are only semi-transparent. After a 2-5x da-ad loopback you can abx the difference, which means, it is also there after a single iteration. The reason for this "surprisingly" good result is that the ad/da runs from the same internal clock, so there will be no effective jitter added during the processing. You cannot save the jitter with the last single DA conversion in the setup. http://www.premiermixing.com SqueezeBox Touch / MacBook Pro -> Audirvana Plus -> Firewire -> Mytek Stereo192-DSD -> GAC1 Pro -> Luxman L-410 -> Rubicon RP63F SqueezeBox Touch / MacBook Pro -> Audirvana Plus -> Firewire -> Mytek Stereo192-DSD -> GAC1 Pro -> DIY Headphone Amp -> Beyerdynamic T70 / AKG K500 / Sennheiser HD540 / Shure SRH840 Mac Pro -> Audirvana Plus -> Lynx AES16 -> Lynx CBL-AES1605 -> Lynx Aurora -> Mogami 2932 XLR -> M-Audio EX66 Link to comment
untangle Posted July 17, 2013 Share Posted July 17, 2013 Loopback testing is common in the pro world, represented by the Gearslutz forums. Here is an example. Bob Link to comment
alexwgoody Posted July 18, 2013 Author Share Posted July 18, 2013 Forgive me if I'm just not exactly getting it- but my understanding is that the loopback testing is done using the same box for both the A/D and D/A conversions. Part of my reasoning to do this is to add a multichannel processor to my current miniDSP 10 x 10 (through analog in)- so while the miniDSP does do an A/D D/A within the same box and clock, the surround processor will have to do a D/A of it's own- which is run by the clock/DAC of the processor. So in effect I would have two pieces of gear with different D/A chips and clocks converting the signal and don't want it to sound like shit/not worth the money. to map it out: hdmi source to surround processor----analog out from processor to analog in of miniDSP for digital crossovers/room correction----then analog out to amps/speakers. This is not quite loopback testing, no? Tell me if I'm being an idiot and I'll take your word for it and move on... Link to comment
untangle Posted July 18, 2013 Share Posted July 18, 2013 A typical loopback test for your use case would quantitatively examine the accuracy of the miniDSP in performing the A/D->D/A task (with no signal processing in play). The figure-of-merit is often the ratio (in dB) of the error term magnitude to the signal. Better converters produce better numbers. The audibility of the differences is disputed, as usual. Bob Link to comment
alexwgoody Posted July 18, 2013 Author Share Posted July 18, 2013 Excellent, thank you very much gentlemen. I look forward to adding multi-channel audio to my stereo. Link to comment
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