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In Reply to: RE: well Charles... posted by Jim Pearce on June 03, 2017 at 13:01:40
>> By transmitting a pair of differential signals, the balanced output provides better common-mode noise rejection and improves signal quality." <<
Yes that is true for specific situations, that are mostly found in recording studios and not home playback systems. My experience is that the common-mode noise rejection of the signal input is not nearly as important as the fact that *differential* balanced circuitry will also provide the same type of rejection to imperfections in the power supplies. The importance of power supply quality becomes apparent when one realizes that the audio circuitry (indeed *all* electronic circuits) are various types of ways to modulate the power supply. Just as with computers, garbage in = garbage out (GIGO). Hence the importance of power supply quality. Differential balanced circuits add an entire extra level of rejecting imperfections in the power supplies.
>> The dedicated L,R RCA outputs sound better than the L,R front 5.1 <<
For the Oppo players this is certainly true of the measured performance. They normally use an 8-channel DAC chip for the 7.1 analog output, whereas the dedicated stereo outputs typically parallel 4 DAC chip channels for each stereo channel. This improves the S/N ratio by 6dB, assuming all else is held constant. Oppo may also use better parts and or power supplies on the dedicated stereo channels (they may be too expensive to use for all 8 channels, just as most customers use higher quality main speakers than surround speakers).
>> I use the xlr outs to defeat bass management in the player without having to dive into the menu. <<
That's fine for all CDs, but it turns out that there are some DVDs that were authored improperly with regards to bass-management. The normal 2-channel mixdown will *not* recover the bass on these discs if you have an HT-2.0 or HT-2.1 system. Ayre added a feature on the DX-5 to correct for this, as described in the owner's manual. To the best of my knowledge, this is the only Blu-ray/DVD player in the world with that feature. Hope this helps.
I play all MC discs in MC mode through the 5.1 analog outputs. I thought it was generally accepted that most common-mode noise comes from the power supply.
If you are not mixing down to stereo, there is no problem created by improperly authored video discs.
> > I thought it was generally accepted that most common-mode noise comes from the power supply. < <
There is at least one other source of common-mode noise found in all digital products - switching noise from the DAC chip itself. With each new sample the output switches to a new state. Real world devices are imperfect and have parasitic capacitances, such that some of the electrical energy used to turn the individual DAC switches on and off is coupled into the audio output signal. Using either two single-ended DACs or one balanced output DAC per audio channel means that the switching noise will be the same in both phases. If the first analog stage is a true differential balanced design, it will reject the common-mode switching noise from the DAC chip. (This is akin to what happens in the recording studio where a low-level microphone signal picks up line frequency hum from the AC wiring in the studio walls equally in both conductors of the balanced mic cable.)
As always, only my personal opinion and not necessarily that of my employer or dog-catcher.
Will the ESS minimum phase slow filter on the Oppo 205 likely approximate what you have done with "MP"?
> > Will the ESS minimum phase slow filter on the Oppo 205 likely approximate what you have done with "MP"? < <
Good question, but hard to say with any certainty. The only real way to know is with listening tests, but there is enough information that we can say "probably not". Although both are described as "slow rolloff, minimum-phase digital filters", there are many differences we can see and likely more that we can't see. About the only visibility I have into the ESS filter comes from the datasheet, which is not publicly available. It shows graphs of both its frequency response and its impulse response. Based on that alone, there are significant differences between the filters. Ayre's single-rate slow rolloff MP filter has about 1-1/2 cycles of post-ringing, while the ESS has about 4-5 cycles of post-ringing.
We have a few data points to help us predict the audibility of this difference. Ayre DACs with a "Listen"/"Measure" filter selection allow the choice of two minimum-phase filters, one with about 20 cycles of post-ringing, the other with 1-1/2 and the difference is fairly easily noticed. In contrast when JA recently reviewed the Meridian Ultra DAC (link below), he found it virtually impossible to hear any differences between minimum-phase filters, the shortest with about 6-7 cycles of post-ringing and the longest with ~35 cycles of post-ringing. Based on these two sets of data points, I suspect that the filter length alone would create an audible difference between the filters. However I also suspect that the slow rolloff MP filter in the ESS DAC chip would be my preference of the 7 choices offered.
That is just the tip of the iceberg, however. While the digital filter is one part of the design that affects the sound, there are many other aspects to digital filter design not mentioned above, including the window shape, the dithering applied, the interpolation rate (ESS uses 8x, while Ayre uses 16x). Further there are many more factors that affect the sound of a D/A converter In my experience, digital filters are one of about a half-dozen major design aspects that will significantly affect the sound of a digital product. Also important are the analog circuitry, the power supplies, the clock implementation, the DAC chip itself, and the presence or absence of any DSP algorithms (such as Asynchronous Sample Rate Conversion - ASRC - and many others). I would be loathe to rank the importance of them, but would agree that the digital filter (or lack thereof, in the case of "non-oversampling") plays an important factor in the overall sound quality.
As always, strictly my own opinions and not necessarily those of my employer or trash collector.
> when JA recently reviewed the Meridian Ultra DAC (link below), he found it
> virtually impossible to hear any differences between minimum-phase filters,
> the shortest with about 6-7 cycles of post-ringing and the longest with ~35
> cycles of post-ringing.
My comment was made auditioning a 192kHz file, whereas my impulse response
measurements were made with 44.1kHz data. After the review was published,
I was told that the Meridian's filters behave differently at 2Fs and 4Fs rates from
how they do with baseband data. I had assumed they were the same at all rates.
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