Receivers redigitzing analog signals for subwoofer

[timetohunt]

This issue/question has come up in various threads usually as a sidebar. I was hoping to get a definitive answer for my curious mind. Lately I have posed this question to about 8 folks, some being customer support people, others audio enthusiasts. So far, the responses are divided right down the center one way or the other.

Its a receiver based question. And for this question forget about 'Pure Direct', because it may come up here and I know how that works and its not directly relevant to this question.

Here goes. Lets say you have a CD player (that has its own DACs) connected to your receiver via analog connects. You also have a subwoofer in your system with basic sub settings on the receiver, 80Hz xover etc. For the purpose of this question, the analog connects are your only link, no digital s/pdif. Your receiver is set without any surround effects and you are NOT using 'pure direct'. Just your signal selected to analog or in this case since you only have analog connects even with the reciever in AUTO its going to choose analog as your source.

The question is this: The receiver will output sound to your subwoofer. SO, WILL THE RECEIVER REDIGITIZE THE SIGNAL IN ORDER TO GET SOUND TO THE SUBWOOFER - OR - DOES THIS STAY IN THE ANALOG DOMAIN. In other words, even though your player has already done a digital-to-analog conversion will the receiver have to do an analog-back-to-digital conversion in order to parse out the low frequencies to get subwoofer sound, or can it derive the necessary low freq material from the analog signal without 'perverting' your original analog signal.

Again, I have asked this many times and it seems to come up 50-50, so I still don't know. My guess is that it does have to redigitze. Even though that is unfortunate - because you are not even really using those hi-priced player DACs (if you have an expensive player that is - and might have well just sent it digitally in the first place, say through coax or toslink). I think a lot of folks may also have spent large money on analog connects and they don't really get used.

Thanks. Really interested to hear what folks here have to say.

NOTE: Depending on the true answer to this, it could bring up a similar more general question. UNLESS you are in 'PURE DIRECT' the receiver will ALLWAYS do an analog-to-digital conversion with an analog signal. Y/N ?

NOTE: this applies to any 2 channel source, but I figured CD would be the most common situation.

 

[j_garcia]

I am sure that would be specific to the receiver, but I am fairly certain that my receiver passes it as is with no conversion for multichannel. Few receivers actually manage the multichannel analog inputs - the signal is presumed to already have been processed, though I know there are some receivers out there that are capable of doing this.

So if you connected to the R&L of the multichannel inputs, then the signal more or less could not be processed as is the case with my receiver - that means no bass management at all (besides output levels) is available on those channels. On any other analog input, I can apply bass management, and that would suggest processing is going on.

 

[FatStrat85]

I think typical receiver bass management is a digital process. The Outlaw RR 2150 has analog bass management, but I believe that is fairly rare now. A typical Yamaha/Denon/Marantz/Onkyo receiver probably has to convert that analog input into a digital signal to output to the subwoofer. That's why there is no subwoofer output in Yamaha receivers set to "pure direct" mode. It only passes analog and PCM signals unprocessed. Bass management on a Yamaha requires digital processing. You might be better off connecting your CD player to the receiver digitally and using the receiver's DACs.

However, I'm no expert. I'm sure one of the experts here will be able to offer a more definitive answer.

 

[audioman00]

no way that it's digital, that makes no sense to re convert the signal again, even in car audio decks, the subwoofer output is low-passed by analog circuitry. There would be no real advantage that I can see to converting the signal, after the DAC or CDP has done so... The receiver will simply low-pass the signal and volumize it. The bass management is integrated into the digital based pre-amp in the receiver, but still maintains an analog signal. IMO

 

[cubbie5150]

Great question!! I've posed similar ones on various forums, and to customer service people at Cambridge Audio too (I currently use a Azur 540R in one setup). As far as the Cambridge Audio units, the CS people's responses have been cryptic at best. When using the standard R+L analog input, w/ my sub also in the mix AND w/ the sub using it's own internal crossover, I still think the 540R does an ADC/DAC process. The 540R does not have "Pure Direct"--it offers a "Stereo" setting, & "Direct In" inputs on the back panel. Cambridge CS will only say that if I want unadulterated analog, I should connect my source via RCA to the R+L connectors of the 6.1 channel "Direct In" inputs. HOWEVER, by doing that, I have no sub output--regardless of whether I use my sub's internal crossover. Anyways, this is one of the many reasons why I am moving to a 2-channel amp & pre--I want to use my external DAC w/out worrying about whether a receiver is messing w/ the signal. 2-channel is important to me; I could not give a crap less about multi-channel, DSP or other sound effects.

 

[j_garcia]

A question to yours timetohunt: Where exactly are you going with this one? I understand the question, but just curious as to why it matters, especially for the bass region of sound? Sound quality? If it sounds good, does it matter if it is processed digitally or in the analog realm? IMO, the lowest octaves would probably be the least affected by processing, at least in terms of overall sound quality, as long as no special filtering is going on.

 

[fmw]

Receivers do not have ADC's. What goes to the sub from a receiver is an analog signal. The bass content can arrive from the source in either a digital or analog form and the receiver's options and methods for processing it may differ depending upon the way in which it arrives. However, the ouput to the sub is always analog.

 

[j_garcia]

Receivers that have digital bass management would have to have ADCs would they not? I know of only a few that do this though.

 

[timetohunt]

Well. I don't think we have got this thing yet. I think its a fundamentally imporant question for anyone who wants to know how their receiver works.
I wish we could get someone who builds receivers to provide a writeup.

This is from Matt Whitlock. I don't know much about him other than he write audio articles. And he is on the 'It Digitizes' side.

"Bass management happens in the receiver. Audio signals are processed in a digital domain, where the receiver can determine, in real-time, what audio frequencies make up the input signal, and what speaker they should be sent to. Those in the know would ask how signals can be processed in the digital domain when they are input via an analog connection. Simple. The receiver uses an analog to digital converter to convert the incoming analog signal into a digital one. This means that bass management can be applied to every audio source you own, including an 8-track player if you have one."

http://www.monstercommunity.com/article/10167/The--Bassics--of-Bass-Management

 

[FatStrat85]

Well. I don't think we have got this thing yet. I think its a fundamentally imporant question for anyone who wants to know how their receiver works.
I wish we could get someone who builds receivers to provide a writeup.

This is from Matt Whitlock. I don't know much about him other than he write audio articles. And he is on the 'It Digitizes' side.

"Bass management happens in the receiver. Audio signals are processed in a digital domain, where the receiver can determine, in real-time, what audio frequencies make up the input signal, and what speaker they should be sent to. Those in the know would ask how signals can be processed in the digital domain when they are input via an analog connection. Simple. The receiver uses an analog to digital converter to convert the incoming analog signal into a digital one. This means that bass management can be applied to every audio source you own, including an 8-track player if you have one."

http://www.monstercommunity.com/article/10167/The--Bassics--of-Bass-Management

That is exactly how I would imagine it would happen. It also sounds like the easiest and cheapest way for it to happen since all that digital processing technology has to be in the receiver anyway. My guess is that unless they advertise specifically otherwise, they will probably always go for the easiest and cheapest way to do something (not that digital bass management is a bad thing).

 

[timetohunt]

A question to yours timetohunt: Where exactly are you going with this one? I understand the question, but just curious as to why it matters, especially for the bass region of sound? Sound quality? If it sounds good, does it matter if it is processed digitally or in the analog realm? IMO, the lowest octaves would probably be the least affected by processing, at least in terms of overall sound quality, as long as no special filtering is going on.

Its audioholics isn't it? And its in my nature to wonder about things like this.

I think its important to some degree. A lot of money, brains and effort went into making equipment to create an analog output a certain way that is intended to go unmolested to your ears. Whether some people can hear the difference on not. It also could be important in educating potential audio gear buyers. I could imagine someone saying "if the signal is always going to be reprocessed by my receiver, I will just buy the cheapest data transport and connects I can find". What difference will it make how high of quality the analog equipment is if its just going to wind up the same. Is there anybody here with me on this?

 

[timetohunt]

Receivers do not have ADC's. What goes to the sub from a receiver is an analog signal. The bass content can arrive from the source in either a digital or analog form and the receiver's options and methods for processing it may differ depending upon the way in which it arrives. However, the ouput to the sub is always analog.

fmw,
you may have read the post a little too quickly. Its not at all about the output from the AVR to the sub which ofcourse is analog. Its whether or not an analog signal has to be redigitized in order to produce subwoofer output.

 

[mtrycrafts]

Well. I don't think we have got this thing yet. I think its a fundamentally imporant question for anyone who wants to know how their receiver works.
I wish we could get someone who builds receivers to provide a writeup.

This is from Matt Whitlock. I don't know much about him other than he write audio articles. And he is on the 'It Digitizes' side.

"Bass management happens in the receiver. Audio signals are processed in a digital domain, where the receiver can determine, in real-time, what audio frequencies make up the input signal, and what speaker they should be sent to. Those in the know would ask how signals can be processed in the digital domain when they are input via an analog connection. Simple. The receiver uses an analog to digital converter to convert the incoming analog signal into a digital one. This means that bass management can be applied to every audio source you own, including an 8-track player if you have one."

http://www.monstercommunity.com/article/10167/The--Bassics--of-Bass-Management

I would tend to agree with Matt. But, If your receiver has a 'pure direct mode'
it would be easy to see if in that mode it still sends signals to the sub or not. If it doesn't, then you know or a good probability that that receiver would re-digitize the signal when you deselect the pure digital to process the LFE and for prologic type effects.

 

[markw]

Wow! AVR's digitize analog signals in order to process them digitally! Hooda thunk it! It's kinda like finding out there's no Easter Bunny.

A simple solution to guarantee an analog signal and still use a subwoofer is to connect it (the sub) via either speaker level connections or possibly between the preamp and main amp. In both cases one would use the crossovers in the subwoofer iteslf.

 

[FatStrat85]

This is only important if you believe that the DACs in your source components (CD player, etc...) are better than in your receiver. I think it's smarter to simply spend the extra money on your receiver so it has good DACs. Then you don't have to worry about about the sound quality of all your other components, only their features, since they will be set up to connect digitally to the receiver (therefore making the sound quality of the components a moot issue since digital is digital). I'd rather spend a lot of money on one component that determines the sound quality of all the other components in my system, rather than spending extra money on every individual source component to ensure that they all have excellent DACs. My Yamaha has Burr-Brown DACs, so that's good enough for me. I connect everything digitally to the receiver and have peace of mind. I only have to worry about my other components' features, not their sound quality. I think this saves me a lot of money and a lot of stress.

 

[fmw]

Receivers that have digital bass management would have to have ADCs would they not? I know of only a few that do this though.

No. They don't do digital bass management with analog signals. They do digital bass management with digital input. They just send the analog along to the sub where the sub's crossover takes care of the low pass work.

 

[MDS]

No. They don't do digital bass management with analog signals. They do digital bass management with digital input. They just send the analog along to the sub where the sub's crossover takes care of the low pass work.

An easy way to verify that that is not the case is that many subs have a dedicated input that bypasses the internal xover or a switch you can flip to bypass the xover (like my SB12-plus).

If there were no ADC and the receiver offers multiple xover settings, as they all do, it would need multiple analog filters - one for each xover frequency.

 

[timetohunt]

No. They don't do digital bass management with analog signals. They do digital bass management with digital input. They just send the analog along to the sub where the sub's crossover takes care of the low pass work.

I wish you were right. But as I look further into this I am starting to be convinced otherwise. I think you and I have the same receiver as well and I think it falls into the re-digitizing catagory (I remember that you had the VSX92 Elite from an old thread).

 

[WmAx]

I would imagine it would be rare to find a feature-rich modern surround receiver that does not convert the analog signal to the digital realm. The only cost effective way to offer a great deal of processing effects to all of these channels, such as delay, variable crossovers, multi-band EQ, is to process digitally. This is why most receivers can NOT do these various effects when you use them in a 'PURE DIRECT ANALOG' or whatever name they use for this 'direct' mode if they have such a feature.

But is this important in reality? The answer is a definite NO. A good ADC-DAC conversion has less artifacts and a greater S/N ratio as compared to most common all-analog processing. If you are worried about the sound getting to your ears 'molested', as someone put it, look at the 3rd rate speakers one is probably using. It is rare that anyone uses good speakers that offer little alteration of the signal relative to human hearing ability, sent to them(such speakers in the retail market seem to cost over 10,000/pair for the best value select models capable of such, and usually much more), and no speaker in the world can offer the minute level of 'molestation' as produced by a decent ADC-DAC process.

-Chris

 

[mtrycrafts]

No. They don't do digital bass management with analog signals. They do digital bass management with digital input. They just send the analog along to the sub where the sub's crossover takes care of the low pass work.

And what if you connect a passive sub with an amp at the LFE out? You get the full bandwidth? Most likely not the case at all.