Auditioning DAC in Bypass Mode

[chanlon]

Hello all.

I have an Arcam rDac at home connected to my Rotel 1570/1077 combo.
Connected to the Arcam via toslink is an Apple TV 1st generation. The analog output of the Arcam is connected to the Rotel input via RCA cables.

Now for my questions....
I want to get a true comparison of using the Arcam Dac vs the internal Burr Browns of the Rotel. I don't want to use the D/A converter in the Rotel at all for this comparison.

What is the difference of using the bypass input (7.1 analog input) VS using the tape input with bypass selected? Is there a difference? Furthermore, if I select "Stereo" mode when using the tape input, does that engage the internal Burr Brown DAC?

What would be the difference if WHEN USING THE 5.1 Bypass connection, I turned on LFE re-direct. Does this engage the Burr Brown DAC?

Sometimes I like to use my B&W ASW675 sub when listening to 2 channel audio. I guess what I really want to know is, is this possible using just the rDac DAC and not the Rotel also?

Thanks guys for all your help.

[madmac]

All I can tell you is that the only time you will have zero digital processing with the Rotel is in "stereo Bypass" 2 channel mode.

[srb]

Furthermore, if I select "Stereo" mode when using the tape input, does that engage the internal Burr Brown DAC?

Yes, selecting "Stereo" mode on an analog input engages digital processing. Selecting "Analog Bypass" does not.

What would be the difference if WHEN USING THE 5.1 Bypass connection, I turned on LFE re-direct. Does this engage the Burr Brown DAC?

From Page 21 in your manual, "The LFE Redirect feature duplicates the seven main channels, sums them, and sends this mono signal through a 100Hz analog low filter to the subwoofer output. This provides an unaltered analog bypass for the seven main channels along with a subwoofer signal derived from those channels."

Although some people have said they think an analog signal sounds a little better through the Multi analog inputs than any of the stereo analog inputs, the real advantage to using it in your situation is to be able to derive a subwoofer output without digitally processing the analog input, like engaging Stereo mode to get subwoofer output would on a stereo analog input.

The only caveat is that you don't have any control of the 100Hz low pass filter, and your mains get a full range signal.

Steve

[chanlon]

Thanks, this makes sense to me. The addition of my B&W sub, does add a nice punch to my main speakers.

[madmac]

I'm not sure if that is correct!. I would check with Rotel on that. If you are running a 5.1 on the Rotel via the multi inputs, there is likely some digital processing happening there. I believe it is only in 'stereo bypass' 2 channel stereo where you are bypassing digital processing altogether.........not that digital processing is a bad thing....which it's not!!.

[srb]

No, it's correct. That's why on the Multi inputs you aren't even able to select any of the surround modes and you can't set any speaker levels, delay or crossover points. The only option is a 'cloned' LFE redirect to a subwoofer.

Digital processing is not a good thing if you're taking a digital signal, converting to analog through a DAC, then re-digitizing it again through an ADC and back to analog again through another DAC.

Steve

[chanlon]

I contacted Rotel in regards to my question above. For processing (or the lack of) the 7.1 bypass and standard analog stereo inputs in bypass mode are similar, and neither will pass through the internal DACs of the RSP-1570.
If I want to use a sub with no internal DAC being used, the 7.1 input is the only option. But of course, I get full range to my speakers and under 100 hz to sub.

Just as SRB had mentioned.....

Thanks everyone for the discussion.