Enhancements to Bass Management in SP-1.7

nicolasb · « **on:** 11 Aug 2003, 12:23 pm »

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recognize that most of the "options" or "features" that some customers want are not availabloe on the SP1.7 because the design goal was - build a state of the art 7.1 preamp that did not compromize sound quality.

I'm more than happy to recognise that - but by the same token, we don't know what's possible and what isn't if we don't ask! If we'd all assumed that there was a technical reason why one couldn't separate THX post-processing from Dolby Digital EX decoding and thus not asked about it, then maybe we would never have have got that option. Seems to me it can't hurt to ask, so long as we're happy to accept that the answer will very often be "no, not possible"- which I am.

Another possibility: I like the way the SP1.7 can store different speaker configurations on a per-input basis, so that you could (say) have your front speakers default to Large for CD but to Small for DVD. Could the cross-over frequency also be stored per-input rather than as a single value for all sources, so that I could default to (say) an 80Hz cross-over for DVD but a 60Hz cross-over for CD?

James Tanner · « **Reply #1 on:** 11 Aug 2003, 02:24 pm »

Hi,

Apparently the DSP will not allow for independent bass management at this point but as the computing power of the DSP's get better as we go along it may be something we can do in the future.

james

nicolasb · « **Reply #2 on:** 11 Aug 2003, 04:36 pm »

James,

It sort of sounds from your answer as though you might have thought I meant different cross-over frequencies for different speakers at the same time (e.g. different for fronts and rears). Just to clarify, I meant different cross-over frequencies for different inputs.

At the moment when setting speakers to be large or small we can do something like this:

DVD Input Settings
Fronts: small
Centre: small
Rears: small
Sub: yes

CD Input Settings
Fronts: large
Centre: none
Rears: none
Sub: no

I wondered if the cross-over frequency could be changed from something that is universal to all inputs (like speaker distance) to something that is held separately for each input (like whether a speaker is set to Large or Small).

James Tanner · « **Reply #3 on:** 12 Aug 2003, 07:50 pm »

Hi nicolasb

Yes, as I understand it the computing power required for the different crossover points apparently is quite high so to offer it on each input separately would require a change in the DSP. It is certainly something we will look into in the future.

james

thomaspf · « **Reply #4 on:** 12 Aug 2003, 10:09 pm »

@nicolasb

Isn't your setting possible today? What happens if you set your CD input to digital in with pass-through mode and xbass turned off.

Does'nt this mean your 2 fronts will get the full range signal independent of the speaker size setting and the sub is turned off.

I am in the office right now but I think this is how I ended up using it for the digital output from my PC. In this mode the 1.7 works pretty much like a 2-channel DAC.

Cheers

Thomas

James Tanner · « **Reply #5 on:** 12 Aug 2003, 10:42 pm »

Hi Thomas,

Yes - but if you are using bass management and have the crossover set at say 80 Hz then that is a universal setting if you want the sub to be in the system on other inputs.

james

thomaspf · « **Reply #6 on:** 13 Aug 2003, 05:39 am »

I am aware of the single crossover frequency. However for the 2 scenarios nicolasb has posted one is with sub and the other one completely without.

Would my settings work?

Thomas

nicolasb · « **Reply #7 on:** 13 Aug 2003, 09:59 am »

Thomas,

You can already do what I was suggesting apart from the per-source cross-over frequency - you can have the DVD input treat the front speakers as Large, but the CD inout treat them as small, for example, or have the DVD input treat the speakers as small while the CD input defaults to 2-channel analogue bypass.

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as I understand it the computing power required for the different crossover points apparently is quite high so to offer it on each input separately would require a change in the DSP

I must confess I don't understand why the use of different cross-over frequencies for different inputs would require more computing power, because you're only using one value at a time. The calculations the DSP would be doing while you're listening would be unchanged.

Consider the following sequence:

1) Listen to something with an 80Hz cross-over.
2) Go into the menu and change the cross-over to 60Hz.
3) Switch inputs.
4) Listen to the other source with a 60Hz cross-over.

If you were to store the cross-over frequency against the input then stage 2 dissappears, but stages 1 and 4 would be exactly the same in terms of the calculations the DSP is doing.

Maybe there just isn't anywhere to actually store the values? Lack of memory, or too few registers?

James Tanner · « **Reply #8 on:** 13 Aug 2003, 11:36 pm »

Hi nicolash,

I will pass your comment on to one of our digital engineers for comment.

james

nicolasb · « **Reply #9 on:** 14 Aug 2003, 12:35 pm »

Cool! I probably don't know what the hell I'm talking about, as usual, but it's always interesting to know where one is going wrong.

Incidentally, in case anybody is wondering why on earth I would want to have different crossover frequencies for different inputs in the first place (given that the actual frequency response range of the speakers would be the same in each case) this comes back to the business of losing everything above the crossover frequency in the LFE channel when playing back 5.1 or 6.1 recordings.

Because this happens, even if your main speakers are quite comfortable going well below 80Hz, you really have to set the crossover to at least 80 or you lose LFE. But when listening to material without a dedicated LFE channel (e.g. stereo music) it might sometimes make sense to cross over at 60Hz or even lower.

James Tanner · « **Reply #10 on:** 14 Aug 2003, 01:05 pm »

Valid point - I set my system at all speakers large and .1 channel at 120Hz in order to replicate the studio recording.

james

nicolasb · « **Reply #11 on:** 14 Aug 2003, 03:07 pm »

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I set my system at all speakers large

That's nice if all 7 of your surround speakers are Linn Keltiks, but very few floorstanders are really full-range. DD and DTS can go down to 20Hz in all the main channels, and stereo music can go even lower - a big pipe organ has a lot of very high volume stuff going on as low as 16Hz. Very few non-subwoofer speakers can handle that convincingly.

James Tanner · « **Reply #12 on:** 14 Aug 2003, 03:17 pm »

Hi,

It is not really true that the rears and centers get 20Hz material.
Very few studio engineers mix low frequencies to the rears or for that matter the center. Especially with movie soundtracks.
The phase issues are very much an issue when you have all channels with low bass. Most mixes put the bass in the .1 or the Left/Right.

james

nicolasb · « **Reply #13 on:** 15 Aug 2003, 09:59 pm »

A similar possiblity that occurred to me today: the different sources I'm using all have slightly different volumes. Switching from one to another invariably requires me to adjust the volume, and occasionally deafens me if I switch from a quiet to a loud source without thinking. Could the SP1.7 (optionally) remember what the volume setting was the last time a particular input was used, and default to that when you switch inputs?

Or could you perhaps even store a volume offset for each input so that if you're listening at a given level for a quiet source and you switch to a loud source that has a -5dB offset value, it automatically pushes the overall volume down by 5dB as it switches?

James Tanner · « **Reply #14 on:** 15 Aug 2003, 10:14 pm »

Hi nicolasb,

I am not sure on that one - I will speake to our software engineer.

james

nicolasb · « **Reply #15 on:** 5 Sep 2003, 10:43 am »

James T,

I wondered if you had read Meridian's interesting take on the room correction issue? They specifically eschew the idea of trying to flatten the room's frequency response curve, and instead use notch filters which (they claim, anyway) a) has the effect of also correcting in the time domain, and b) does NOT suffer from the problem of only being correct for one specific listening location.

See http://www.meridian-audio.com/w_paper/Room_Correction_scr.pdf

stp1200 · « **Reply #16 on:** 10 Sep 2003, 09:02 pm »

Let me try to clear some things up. We know that the SP1.7 only has enough processing power for one crossover point at a time. This is a global setting for all speakers defined as 'Small' and is currently enabled as a global setting for all input.

Contrary to what JT may have indicated, we could switch to a different crossover frequency on an input change, and have that saved as part of the preferred settings per input. I'll consider this for Version 44.

Once you start changing the crossover frequency though, you have to re-run the BPLM routine if you have the BPLM active. And you would have to do that for each input with a different crossover frequency and have that saved with the input settings as well. So we'll have to consider this as well

jethro · « **Reply #17 on:** 21 Sep 2003, 01:26 pm »

Quote from: stp1200

Let me try to clear some things up. We know that the SP1.7 only has enough processing power for one crossover point at a time. This is a global setting for all speakers defined as 'Small' and is currently enabled as a global setting for all input.

Contrary to what JT may have indicated, we could switch to a different crossover frequency on an input change, and have that saved as part of the preferred settings per input. I'll consider this for Version 44.

Once you start changing the crossover frequ ...

Shane, James:

Wouldn't it also be necessary to include the saving/loading of output levels for all speakers per source ? I assume that when the sub-woofer crossover for a particular input is changed that it may affect the output level of all speakers. The manual says that only the surround and back levels are saved per input.

FWIW, I think the addition of a sub crossover for each individual source would be very useful in my setup.

Thanks, Steve

stp1200 · « **Reply #18 on:** 25 Sep 2003, 02:32 pm »

Since the manual was printed we've added a couple channels to the save function. As of version 43 (i think, i'll have to check the docs), you can save the Centre level and Subwoofer level for each input.

I'm trying some things out right now with version 44 that include the crossover save function that you are asking for. The tricky part is making sure it all comes together properly with the BPLM.

I wonder how people feel about having to run the BPLM routine and save it for each input?

jethro · « **Reply #19 on:** 27 Sep 2003, 11:19 pm »

Hi Shane,

Personally I don't use BPLM because I have a passive sub (without crossover) and the SP 1.7's test tone is full-range which my sub doesn't like very well. However if I had an active sub, I would find running BPLM for each input a minor inconvenience. To me the separate crossover per input far outweighs having to run BPLM for each input. The other advantage of having more of the parameters for the system saved on a per input basis, makes it easier for the user to remember how the system works - i.e. more uniform. The user doesn't have to second guess whether changing a parameter and/or hitting the "save settings" button on the remote will affect the setup for other inputs.

If you get have the non-volatile storage space can we get the mods to save the left and right channel levels as well ?

Thanks, Steve