I've been a religious 2-channel music listener but have recently been playing around with Dolby Prologic IIx Music instead. I have to admit, I think I prefer it now that I've dialed in the front soundstage.

However, I've noticed that the bass signal sent to my subwoofer in DPIIx Music is at least 6-10 dB stronger than the signal sent to my sub when playing 2-channel stereo (either Bypass, Upsample of Stereo). I need to trim my subwoofer settings when I switch to DBIIx Music by a fair bit to reduce the signal by 6-10 dB.

Does anyone have an idea why this is happening? Do others experience this? Is it a quirk with DBIIx Music?

I'm surprised by this experience, especially considering that DBIIx Movie doesn't seem to "pump" the subwoofer signal.

Any ideas?

Thanks in advance!

Bryan

Sounds odd. Dolby PLllx shouldn’t effect your bass output, AFAIK that is still being handled by your receiver’s bass management system even when DPLllx is enabled. Sounds like you might have an outlaw 990 which does have the capability to attenuate the subwoofer signal by up to 8dB when in stereo mode for music. Perhaps that’s been enabled and for some reason when you switch to DPLllx it’s cutting out and sending the full signal to the subwoofer.

Sorry if that isn’t much help but what you describe shouldn’t be happening.


How did you get the front soundstage dialed in. I just can’t get it to sound right for some music. Works great for classical concerts and ambient music but with good studio recordings it makes the front soundstage seem flat or compressed. For a long time it made vocalist sound 5 feet wide until I figured out the default settings spread out the center information. Even though I’ve gotten the soundstage balanced out I just can’t get past the tonal differences it’s causing in the front soundstage.

grunt,

It is odd! I do have the Outlaw 990 but I don't have any attenuation set for stereo, 2-channel music. The setting is at 0dB and doesn't cut the subwoofer. However, it's possible that the signal sent to my sub in 2-channel stereo is too weak and that the signal in DBIIx Music is correct? But it definitely sounds a bit boomy when I switch to DBIIx Music.

I have to admit that I haven't played much music yet via DBIIx Music. For now, all I've really played is some country (i.e. Dixie Chicks) and some light rock (i.e. Dire Straits, Clapton, Blue Rodeo). I widened the front stage by setting the Center Width to 5. Previously, it was set at 2 and it seemed to compress the front and route everything to the center channel, which I did not prefer. Setting it to 5 seemed to widen the front stage without diffusing the vocal. Setting it to 6, however, did diffuse the vocals too much and spread them out to wide. I also set Panorama on which also seemed to widen the soundstage but didn't diffuse the vocals.

Admittedly though, I'm not really an audiophile so my ear can't be trusted too much But it does seem to sound pretty good too me - so far.

Bryan, I always use DPLII or another of the ambience extraction modes when listening to 2-channel source material. As Dean pointed out, these modes have nothing to do with the relative level of the subwoofer or other bass material. They detect and extract out of phase material that represents reflected surround ambience, then send it to the surrounds.

I've never experienced anything unusual about the bass levels when using these modes. I wonder if it's actually the sub level or is it the surrounds which are causing the "boomy" effect? I never use the Panorama setting, since that simply takes some of the material that should stay in the front speakers and sends it to the surrounds, sort of a partial step toward "all channel stereo" which I don't care for.

I'm not familiar with any quirks in the 990 which might explain this, but again, it isn't the DPLIIx processing as such. Are you certain that when you were listening without surround in effect that you didn't use a "direct" or "pure" type of mode which didn't send signals to the sub when 2-channel material was being played?

Bryan your not crazy unless I am also (ok my friends would say that’s not much comfort). I just ran a test and can confirm that I am getting an 8dB-10dB boost in the SPL from my subwoofer measured near-field with my radio shack SPL meter when using DPLllx. My mains are showing a corresponding drop measured near-field to the woofers. And that was switching between 2ch stereo+sub and DPLllx all crossovers set to 80Hz in both 2ch and multi-channel modes.

The net effect at my listening position is no change in the SPL so I never noticed this redirection. Is there any chance your subwoofer is near a wall or corner? Neither my subwoofer nor mains are corner/wall loaded so that might explain why you’re hearing the effect so much while I don‘t hear it even though I can measure it. Problem with that is lots of people corner load subwoofers so you’d thing more people would notice it.

If your sub is corner loaded you could experiment by pulling it out 3-4 feet from the walls and see if the bass “pump” diminishes.

Actually, I need to thank you for posting your question because I never really gave cinema mode a chance since it didn’t seem to do much for movies so I used music mode with 2ch movie/TV. I don’t remember trying it on music and am finding I quite like the effect. It definitely enhances the ambience but w/o the seeming flattening out of the highs the way music mode does on many recordings. Matter of fact just finished listening to two of my favorite 2ch SACDs Boston and The Bangles and actually think they sound better in cinema mode rather than 2ch direct.

Cheers,
Dean

Hi Icehawk, grunt, JohnK and all,

Somewhere in my distant memory I read a piece about why this happens with Dolby PLII(x) in the Music mode. The same thing happens on my H/K AV receiver when I switch from Logic7 or dts Neo:6 to DPLII Music mode--a boost of about 6 to 10 dB in the sub level. I can't recall if this is an error in the Dolby algorithm or an error in implementation of the Dolby decoder by, in my case, Harman/Kardon. I know that Dolby licensees are given quite a lot of flexibility in how they install Dolby processing modes in their products.

More research is needed. I still have a contact at Dolby Labs, and at H/K, so I'll send off an email and see what comes back. I think I read about this in a thread on another forum.

There will be an update. . .

Regards,
Alan

What are the xovers for all your speakers?
DBII will remove embedded "ambiance" signals from your mains to distribute it to other speakers. If those speakers do not have the same configuration than your mains (especially if you are using you mains in a full-range or low xover), you might get quite a bit of signals now sent to your sub-woofer that were sent to your mains, especially from your central channel.
That could be an indication (if the difference is THAT big), that your sub-woofer might be configured too "hot" to match your mains only.

Thanks for the replies.

Answers to some of the questions...

I have M60/VP150/QS8/EP500 system. All speakers small, crossovers at 80Hz, except mains (M60) at 60Hz. Sub is not corner-loaded - it is at the end of my couch (about 1/4 length of wall from the far left corner) and the rear of the sub is about 1.5 - 2 feet from the wall.

I've measured my frequency response vis a vis my mains with an SPL meter (and brute force) and actually get a fairly good response. Slight house curve in the sub region (20-60)and a modest increase around 80-100 due to room mode (from my mains). I've never measured the response vis a vis my center and surrounds. This is an exercise I plan on doing in the near future to dial in my crossovers for these speakers. (Note: I don't run REW and have to do it manually with test tones).

JohnK - I run my 2-channel stereo using upsample mode, which incorporates the 990's bass management and sends signals to mains + sub according to settings. This is actually the mode I used when dialing in my frequency response above so I'm quite certain the bass is accurate in 2-channel mode. BTW - I'm not completely sold on Panorama either. I've played with it a bit and haven't really noticed much difference - but this could depend on the source material as well.

grunt - questions answered above. Your welcome for re-connecting you with the music Thanks for confirming (with measurements) that I'm not crazy.

alan - Thanks for the response. I eagerly await the results of the investigation.

EFalardeau - Interesting comments. This could be a reason. My sub is calibrated at the low end (20-30 Hz) to be about 3-5 db hot, with a general roll-off to the crossover.

Bryan

Further to my other post, since it was on my mind, I went and checked the subwoofer settings as well as all the channel-level settings in the ambiance/surround modes as well as in stereo, with the subwoofer on. Sub is set to 0 dB in all modes.

I'm running M22s, two QS8s, an EP500, and a different bookshelf as a center; all speakers set to Small with an 80-Hz crossover.

Here's what I found. Moving from H/K's Logic7 Music mode to DPLII Music mode, the sub level increases by about 6 dB. However, the overall level of the mains, center and surrounds also increases a couple of dB. Put another way, Logic7, compared to DPLII Music, stereo with the sub on, and dts Neo6 music mode, Logic7's level is a few dB lower. Even so, the subwoofer level in DPLII increases significantly compared to dts Neo6 or stereo with the sub on.

Still mysterious.

Regards,
Alan

I knew there was a reason I exclusively use Neo6.

Thanks for taking an interest in this, I’m very curious as to what’s happening so I hope you come up with something.



I was thinking the same thing which is why when I ran my test I reset all crossovers to 80Hz (had my mains set to 60Hz) in both 2ch direct + subwoofer and multi-channel. I also reset all the speakers to the base calibration so nothing was running hot.

To reiterate when I switch between 2ch direct + sub and DPLllx music the overall SPL at the listening position stays the same but the subwoofer‘s output goes up 8-10dB in DPLllx music, in DPLllx cinema there is an overall increase of about 2dB at the listening position. There’s a corresponding drop from the main’s woofers.



I Just tested Neo6 and it’s doing the same thing only it’s upping the subwoofer by 10-12 dB vs Dolby’s 8-10 but just like Dolby the overall SPL is staying the same.

D'oh.

Now what I always do when I'm calibrating DD or DTS (non-Neo6 or PLII) is calibrate the sub 10 dB hotter than the mains. However, that could be an artifact of my calibration disc: the original non-Avia one, whatever that is.

I assume my settings from the DD and DTS carry over to PLII and Neo6, respectively. I could be horribly wrong, of course.

Okay, I punched up the Rachmaninoff 1st Symphony, which has a quite bass-heavy passage about 25 seconds in. I switched between the DPLII Music and Movie modes several times each at the point and measured no significant difference(12" from EP500)with my SPL meter. The Movie mode averaged about a dB higher, but that could simply be measurement error.

Edit: I took more time and ran the same several times each with straight stereo, Neo:6 and Neural Surround(don't have Logic 7 available). All measurements were essentially identical within a dB.