A few questions about DAC basics

Mrowland -

Hmmmm..... You are right, if I use a DAC (or even just the Pioneer DVD/CD analogs) into the EXT IN FL and FR inputs I am missing a signal to the sub.

I wonder if an RCA Y splitter was used to the SUB IN from one of the FR or FL channels to the SUB IN in the EXT IN group if that would work?
This is how the EXT IN RCA group looks:

O O O
FL C FR

O O O
SL Sub SR

The Denon manual seems to imply that the SUB IN jack in the EXT IN group is routed internally to the regular RCA Sub preout jack which is what I am using for the sub now. If I used a splitter the full signal would then be sent to the Sub and it's built in crossover could be used.
The sub itself (ACI Titan) has three line level inputs (L/C/R), but I am guessing that is not what you mean by "That's why you'd need a sub with 2 sets of inputs".
I can get a speaker level input adapter for the sub from ACI, but have never used that before.

How do people using a DAC get a sub signal to their sub?
Is this why Mraybeck has suggested a real stereo preamp above?

Lkdog,
I do feel that getting a dedicated 2-channel preamp will be a significant upgrade in your system. However, even with a preamp, you will still need either a speaker-level input on your ACI (like the RELs), or use line-level input from a splitter (probably will degrade 2-channel sound) or route the entire line-level signal to the sub to use its crossover, and then from the line out of the sub to the amp. This last method also has its drawbacks as you will be running your entire audio signal through another 6+ feet of cabling. This is why speaker-level input is generally preferred for 2-channel audio.
If you are currently using the RCA sub preout for music listening, then I would be willing to bet that your Denon is, in fact, redigitizing your analog signal. The LFE circuitry is done in the digital domain, and I truly doubt that your receiver has a good analog crossover. If you really want to maximize your system for 2-channel and wish to keep the sub, I would get the speaker-level input adapters from ACI. Just my .02

Lkdog,

Nice idea, but there's another problem in addition to the degradation mentioned by Mraybeck. When using the EXT inputs, you'll be running a full range signal to the front speakers, so the crossover setting in the sub that works well this way will not work if you have the Denon set for "small" front speakers! However, as I've said before, my low end Onkyo sigificantly degrades the sound when ANY processing is used (this includes using the crossover via setting the speakers to "small"), so I just leave them full range. The drawback here is that you're wasting power and possibly muddying up the midrange by trying to pump the low frequencies into the small speakers, but life is full of compromises.

By the way, trust me that it won't work very well splitting only one of the channels into the Denon's subwoofer input, because music mixes are too varied (yes, I tried it once). Also, I don't like the idea of combining the left and right because I don't think the output buffer of the DAC would be happy with that.

Many people have had this same problem, so you might do searches here and at the AudioAsylum.com. Many people have tried a separate preamp as per Mraybeck, but it can be a hassle to match the volume of all channels, especially at different volumes.

There are 3 main ways to achieve the use of a sub in your situation.

1) Get a separate 2 channel system. Don't laugh, it's been done by others than your's truly.

2) Get 2 subs. One is hooked up to the LFE channel (you can use the HT receiver's built-in crossovers on everything but the direct pass throughs); the other is hooked up to the preamp outputs (low level) or the amplifier outputs (high level), and its crossover is set to blend with your front speakers running full range.

3) Get 1 sub that has regular left and right channel inputs (low level and or high level) AND an LFE input. As I said earlier, the REL Storm III (and higher models) is the only one that I know of that does this. The crossover must be defeatable on the LFE input if you are using the HT receiver's built-in crossovers, because you will have to set it around 40 Hz for your fronts, but the receiver will probably cross over the fronts at about 80 to 120 Hz.

Just a note. All of this is moot if the HT receiver is able to pull off the low frequencies on the analog pass-throughs. I don't know of any that do this though.

Whew!

Let us know what happens.

You guys have been great.
Let me try and digest this a bit and I will post later today.
Thanks!

Ok. I think the first step is to talk to Denon about the following two basic questions and hope I get a tech that knows what he/she is doing:

1) What exactly happens to a signal via regular analog inputs into the Denon CD or DVD analog inputs for example, when playing two channel Stereo mode.
The manual is unclear but seems to imply that minimal processing is occurring to any signal that is not Dolby Digital or DTS. Although "Stereo" is technically a surround mode, none of the DSP effects are available, nor is the LFE adjustment to the sub available when the signal is non DD, or DTS. In fact the manual later then excludes the Stereo mode as a surround mode when listing them.

The manual is not as explanatory as it could be. It DOES then go on to state that ONLY the Stereo Mode can be used when playing PCM signals with a sampling frequency of 96kHz.
I guess my related question is what would happen to a DAC signal at 24/96 inputted (manual is unclear as to whether this is an analog or digital signal input) when using Stereo mode; and what does the Denon do to the bass or sub pre out settings in that case.

Here are a summary of the Denon specs from their website:

AVR-1801
Dolby Digital & DTS A/V Receiver • 24 bit DSP processor • 5 equal power amplifier channels • 70 watts per channel into 8 ohms, <.08%THD, 20Hz - 20 kHz • Discrete power amplifier stage • 5 Channel Stereo • Personal Memory Plus • Virtual Surround (for use with 2 speakers) • 24 bit, 96 kHz DACs • 24 bit, 96 kHz digital interface receiver • 24 bit, 96 kHz stereo PCM digital playback • Speaker A/B (front) selector • 6 Channel External Input (for DVD-Audio) with wideband (100 kHz) frequency response • Addressable digital inputs, 2 optical, 1 coaxial • "S" & composite video switching • Banana plug compatible speaker terminals (L, R, C) • Pre-amp outputs (L, R, C, Sub) • Preprogrammed remote control features TV, VCR, DVD codes from other manufacturers

I can set the speakers to "Small" (80Hz cutoff) or "Large" (full range) in Stereo mode, and do some adjustment of the Sub pre out signal, but that is also a bit unclear. I think that possibly if the fronts are set to "Small", then the sub pre out handles anything below 80hz, but I could be wrong about the bass management in this case. I can also set the fronts and the sub to both accept a full range signal and use the crossover on the sub to cut out frequencies above a sub crossover selected frequency. My sub crossover goes from 50-180 hz. It is a pretty fast sub designed for music.
The Denon manual actually suggests doing it this way-running a full range signal to both the fronts and the sub and using the sub crossover to blend with the fronts based upon the range of the fronts. My fronts are rated down to 45 hz.

2) Find out exactly how this EXT IN grouping of RCA ins works. The manual upon further reading clearly states that all surround processing is bypassed and implies that the sub/bass management is handled by supposedly routing the signal to the standard pre-out as I have stated, if it is used, but the valid questions raised here is how to get a sub in signal into that EXT In sub in line level jack without degrading the signal or compromising the FR and FL signals. The speaker level inputs to the sub has some promise here. This could be a way to go.

I could use splitters to combine the FR and FL signals to mono to the EXT IN Sub in, while also running the separate FR and FL signals to their respective inputs. 3 splitters total. (Yuck).
Curiously, I have a Pro Audio Mackie Mixer in my Recording Studio setup and this is actually the way they tell you is preferred to run a line level signal to the sub (use a splitter to combine the full range R and L channels and then to the RCA line input to the sub, and then use the sub crossover.
This is not quite the same thing as a DAC signal split out as stated by you guys, and is probably not a good idea.

I will keep you posted as to what Denon has to say and go from there. Yes, my head is spinning.
Maybe another option is that this urge to get better sound will pass. :>