Q. about bass management when creating DVD-A

[Old Quad Guy]

Right, if you have it use it to get true center channel information for new mixes only.

 

[vimanapc]

I like the centre channel for a lead vocal, and use the other channels for backing vocal or double tracking effects using the stereo imaging of the front right and left channel pair for distribution.

The LFE/Subwoofer dilemma has resulted in many experiments when encoding 5.1 Dolby Digital. I used to try and do the bass management by replicating and eqing tracks. This usually resulted in a muddy mess with very top end sounding channels. (Extremely painfull after a while of listening at higher volumes). Some of the home cinema systems (the cheaper ones that most people buy - the main mass market!!!) handle this type of filtering OK!! with just acceptable results.

I think the solution lies in mixing for full range speakers, then allow whatever a systems bass management is to redirect frequencies away from the satellites to the Sub channel. The LFE should only include very low frequency effects/signals such as sub-bass stuff!!

On the subject of encoding for DD 5.1, what filter cut-off should be used if at all!! 80Hz or 120Hz. Using this would seem to contradict some of the best practises being suggested at the moment for music.

 

[Old Quad Guy]

When and if you do mix for the .1 low end. Are you doing a mono mix of all the other channels combined together and then change the EQ from the mono mix. Or are you just using the low end bass pieces of the music? Do these mixing rules need to be changed depending on different encoding uses (DVD-A, DTS, DD)?

 

[Old Quad Guy]

Sorry, I'm sick with the flu and don't know what the heck I'm talking about.

 

[neil wilkes]

On the subject of encoding for DD 5.1, what filter cut-off should be used if at all!! 80Hz or 120Hz. Using this would seem to contradict some of the best practises being suggested at the moment for music.

According to Dolby, the cutoff should be 120Hz.
However, DTS recommend 80Hz.
I generally filter to 80Hz, with a 48dB/Octave HPF.

 

[Ge Someone]

DTS recommend 80Hz.
I generally filter to 80Hz, with a 48dB/Octave HPF.

For what it's worth, THX (not an encoding standard) also recommends 80Hz for their speaker specifications.

BTW. I assume you mean LowPassFilter for the LFE channel, as you pointed out that you would use full range for the rest .

 

[neil wilkes]

For what it's worth, THX (not an encoding standard) also recommends 80Hz for their speaker specifications.

BTW. I assume you mean LowPassFilter for the LFE channel, as you pointed out that you would use full range for the rest .

Doh!!
Wrong filter. I wondered why things were sounding wrong.


I generally stick to 80Hz wherever possible.

 

[diatonis]

Hi vimanapc,

On the subject of encoding for DD 5.1, what filter cut-off should be used if at all!! 80Hz or 120Hz. Using this would seem to contradict some of the best practises being suggested at the moment for music.

I don't filter it. I let the playback unit select what it wants to do.

This is from the Dolby Digital Professional Encoding Guidelines page 4-19

4.7.4 LFE Lowpass Filter

The LFE Lowpass Filter parameter can be used to activate a 120 Hz low-pass filter applied to the LFE input channel. If the digital signal fed to the LFE input does not contain information above 120 Hz, this filter can be disabled. This parameter is user adjustable only when the LFE channel is enabled.

So if you aren't putting anything into the LFE channel then you don't need to filter anything. If I'm understanding your question

Hi Old Quad Guy,

When and if you do mix for the .1 low end. Are you doing a mono mix of all the other channels combined together and then change the EQ from the mono mix. Or are you just using the low end bass pieces of the music? Do these mixing rules need to be changed depending on different encoding uses (DVD-A, DTS, DD)?

I think what neil and the others are saying is that the bass management system does exactly what you are wanting to do - create a filtered output signal that is sent to the subwoofer. There's really no reason to actually create one as it would only cause phasing problems etc...

I have a few earlier DVD-Audio discs which appear to have a synthesized LFE. Someone has created a mono track from the 5 main channels applied a low pass filter at some frequency say 80Hz? and then decreased it's volume by about -25 dB. NOTE: Anything appearing in the LFE track is amplified by +10dB. This synthesized LFE signal is somewhat low in the mix but its there. I think they did this for two reasons: So the dvd player displays 5.1 and not 5.0 (encoding as 5.1 and not 5.0) as well as to enable some bass to be present when no bass management is used. In the later case the LFE channel is connected directly to the sub . It does seem to muddy things up if I'm using the [SMALL SPEAKER] settings.

 

[ssully]

NOTE: Anything appearing in the LFE track is amplified by +10dB. .

Unfortunately, this does not always happen for 'exotic' signals passed digitally,e.g., other than DD/DTS bitstreams. There's a whole thread about it on AVSforum, and there is some questions as to whether LFE on DVD-A (and SACD, which apprarently does NOT require a 10dB boost) discs are routinely processed correctly or not

http://www.avsforum.com/avs-vb/showthread.php?t=748147

Whilethe issues described in that thread are something DVD-A/SACDphiles have had to deal with already, it's becoming a bigger issue now that we have DolbyTrueHD and Blue-Ray audio, which is decoded in the player and passed digitally as high-resolution PCM via HDMI.

Also, re; the original problem in the first post, I would guess there is a flaw in the OP's bass management -- with rear speakers set to SMALL, any bass content therein SHOULD be routed to the sub.

 

[neil wilkes]

Dolby True HD is MLP by another name, so there should be no difference between any HD DVD that has 5.1 or 7.1 True HD (If such a disc is ever released, of course) and DVD-A with MLP.
In DVD-A players using the analogue RCA outputs, the content is also decoded in the player & output as PCM. It can also output via HDMI.