# DD+, TrueHD Downmixing questions...



## Vader (Jul 8, 2006)

Until the bass management bug in the 1st gen Toshiba players is fixed, I am going back to bitstream via optical, and letting my AVR do the BM. As I was watching Batman Begins this way, I was playing around with the sound formats, and noting the differences between each. My understanding is that Dolby Digital Plus downmixes to full bitrate (1.5mps) DTS, which is then decoded by my AVR, right? Well, my AVR says that the incoming signal is 48Kbps, so what am I missing? Also, when I switched to TrueHD to see what the downmix was, the AVR still said I was getting no more than 48Kbps. Before FW2.0, the Tosh would only send 2.0 PCM out of SPDIF for TrueHD (48, 96 or 192 Kbps). Now that we have TrueHD 5.1, does it send 5.1 PCM over SPDIF? The AVR still interpreted the downmixed TrueHD as DTS, even though it was PCM. Is this normal? Should I be downmixing a lossless track in the first place?

<Jack Tripper voice> I'm so confused...:dunno: <end Tripper vioce>


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## Sir Terrence (Jun 8, 2006)

Vader said:


> Until the bass management bug in the 1st gen Toshiba players is fixed, I am going back to bitstream via optical, and letting my AVR do the BM.


Wow, I own a first generation player, and I am not aware of any bass managment bug. I know the second generation XA-2 has one, but mine doesn't have it. 




> As I was watching Batman Begins this way, I was playing around with the sound formats, and noting the differences between each. My understanding is that Dolby Digital Plus downmixes to full bitrate (1.5mps) DTS, which is then decoded by my AVR, right?


I believe the correct word as opposed to downmixing is transcode, or re-encodes. Yes you are right. 



> Well, my AVR says that the incoming signal is 48Kbps, so what am I missing?


I think it says 48khz, not 48kbps. One is a sample rate, the other the data rate. 48kbps would sound absolutely horrible. However DVD's, HD DVD, and Blu-ray disc(with a few exceptions) are all sampled at 48khz sample rate. 



> Also, when I switched to TrueHD to see what the downmix was, the AVR still said I was getting no more than 48Kbps. Before FW2.0, the Tosh would only send 2.0 PCM out of SPDIF for TrueHD (48, 96 or 192 Kbps). Now that we have TrueHD 5.1, does it send 5.1 PCM over SPDIF? The AVR still interpreted the downmixed TrueHD as DTS, even though it was PCM. Is this normal? Should I be downmixing a lossless track in the first place?
> 
> <Jack Tripper voice> I'm so confused...:dunno: <end Tripper vioce>


There is no way to send 5.1 PCM out over SPDIF input. The digital inputs bandwidth is not large enough to support anything more than 2.0 PCM. The only way to get 5.1 PCM is through HDMI and analog 5.1 inputs. It appears you are mixing sampling rates and data rates up. 48,96,192khz are all sample rates. 640kbps, 1.5mbps are bit rates.


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## Vader (Jul 8, 2006)

> Wow, I own a first generation player, and I am not aware of any bass managment bug. I know the second generation XA-2 has one, but mine doesn't have it.


The Tosh A1 and XA1 both do not boost the LFE by the 10dB standard. This can be addressed by boosting the LFE input at the AVR, but the problem is that the redirected bass (assuming the speakers are set to small in the Tosh) is also part of what the AVR boosts. If the speakers are set to large, there is no problem, other than the lost redirected bass below the FR of the satellites. In essence, the redirected bass is 10dB hotter then the dedicated LFE stuff, so when the 10dB boost is applied, the LFE is corrected, but the redirected stuff is 10dB too hot. AFAIK, this has yet to be addressed by Toshiba, and affects all 1st gen machines. There are workarounds, but none of them are entirely satisfactory. We need a FW upgrade for this...



> I think it says 48khz, not 48kbps.





> It appears you are mixing sampling rates and data rates up.


Yup. My bad...... I'm home sick, so I have an excuse :innocent:



> The digital inputs bandwidth is not large enough to support anything more than 2.0 PCM. The only way to get 5.1 PCM is through HDMI and analog 5.1 inputs.


This is the way I understood it as well, but when I selected TrueHD, and was listening to the digital input, my AVR still said I have a 5.1 DTS signal coming in...?!?


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## SteveCallas (Apr 29, 2006)

Can you honestly even hear a difference between 5.1 PCM and 5.1 bitstream when watching a movie in surround sound? I'm not asking that sarcastically, more so curiously. With music listening, one is focused on the music - for movies, without having listened to a 5.1 PCM track yet, I'd imagine the difference is negligible? :dontknow: The difference in proper bass management would be much more easily noticed.


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## Vader (Jul 8, 2006)

I have not heard a PCM track, but the differences between a TrueHD track and a re-encoded Dolby Digital Plus one is definately significant. There are those who say that LPCM trumps TrueHD, but I'm not sure I buy that (both are lossless). The TrueHD sounds much smoother, more detailed and generally richer. After having listened to Batman Begins TrueHD track and then moving to the bitstream, I definately am gonna miss the TrueHD (but, the bitstream sounds pretty **** good in its own right)


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## Sir Terrence (Jun 8, 2006)

Vader said:


> The Tosh A1 and XA1 both do not boost the LFE by the 10dB standard. This can be addressed by boosting the LFE input at the AVR, but the problem is that the redirected bass (assuming the speakers are set to small in the Tosh) is also part of what the AVR boosts. If the speakers are set to large, there is no problem, other than the lost redirected bass below the FR of the satellites. In essence, the redirected bass is 10dB hotter then the dedicated LFE stuff, so when the 10dB boost is applied, the LFE is corrected, but the redirected stuff is 10dB too hot. AFAIK, this has yet to be addressed by Toshiba, and affects all 1st gen machines. There are workarounds, but none of them are entirely satisfactory. We need a FW upgrade for this...


Okay, this explains why I don't notice it in my setup. The only channels in my system that have BM applied to them is the surrounds. However, when calibrating the subs on my LFE channel, I couldn't see any lack of boost when measuring the output. I did not have to crank up the gain any appreciable amount to obtain a optimum balance. This is output through my six channel analog in's on my Onkyo receiver(pre-pro really). My current setting sits at -3, a ten decibal boost from that would be about +8. A -3 setting is equal to a calibration of +75db. On the 5.1 test disc I have, the LFE setting of -3 corresponded to a proper LFE playback on both DD and Dts, who's proper settings are quite different during playback. 

As far as the re-directed bass being 10db hotter, it looks like the players BM is not appying the -15db pad, and +3 db boost that occurs when the BM is done in the AVR's processor. I cannot see how the internal decoder of the Toshiba passed Dolby and Dts liscensing without the proper cut and boost in the BM. 




> Yup. My bad...... I'm home sick, so I have an excuse :innocent:


Sick sucks. Get well buddy!!!





> This is the way I understood it as well, but when I selected TrueHD, and was listening to the digital input, my AVR still said I have a 5.1 DTS signal coming in...?!?


Okay another mix up here. Dts 5.1 is not PCM 5.1. Dts 5.1 does come from the digital outputs because its lossy, and does not take anymore bandwidth than a 2.0 PCM signal would coming through those outputs. If you use the digital outputs, DD+ and TrueHD are transcoded to full bit rate Dts. That is why you see a Dts signal coming in.


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## Vader (Jul 8, 2006)

> when calibrating the subs on my LFE channel, I couldn't see any lack of boost when measuring the output.


Neither did I, but my Denon accounts for the 10dB shortfall (as is industry standard), and I use DVE (accounting for the LFE error), which uses the LFE channel for the sub calibration, so I would not see any problem (no redirected bass). I would think the problem would be more obvious if something like Avia were used (which uses redirected bass in it's LFE pink noise). In any case, my sub(s) bottomed quite handily when watching "The Matrix: Revolutions" HD-DVD because the bass in the mains is extremely hot and full range. When it was redirected to the LFE output on the Tosh, and then my AVR boosted another 10dB, it ended up burying the needle, so to speak (not good)...



> DD+ and TrueHD are transcoded to full bit rate Dts. That is why you see a Dts signal coming in.


So you are saying that I actally get a full 5.1 (transcoded) DTS signal when selecting TrueHD? I guess I don't see how a 2.0 PCM could be transcoded to 5.1 (sorry to be thick-headed)...


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## bobgpsr (Apr 20, 2006)

Vader said:


> So you are saying that I actally get a full 5.1 (transcoded) DTS signal when selecting TrueHD? I guess I don't see how a 2.0 PCM could be transcoded to 5.1(


The 1st gen Toshiba players (A1 & XA1) and also the 2nd gen HD-A2 must re-encode the internal decoded & mixed PCM audio to legacy 1509 kbps 5.1 channel dts bitstream to send multichannel audio out via a S/PDIF connection (coax or optical Toslink). The reason is that S/PDIF does not allow lossless multichannel PCM audio due to no copy protection (a political/policy decision enforced by content providers). 2 channel linear PCM is allowed over S/PDIF.

HDMI is protected with HDCP so multichannel linear PCM is OK on that.


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## Vader (Jul 8, 2006)

Kewl! Bob, that is exactly what I wanted to hear. When switching between DD+ and TrueHD over SPDIF, I thought that the TrueHD sounded a bit fuller (could just be my imagination), but I wasn't sure what the A1 was doing with the TrueHD. Thanx!


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## MACCA350 (Apr 25, 2006)

Vader said:


> The Tosh A1 and XA1 both do not boost the LFE by the 10dB standard.


Just wanted to note that this part is not a problem with the player, the player is performing this part correctly. The reason is because the DD and DTS standard allows for an extra 10db on the LFE channel when compared to the main 5 channels, so to do this the LFE channel needs to be boosted somewhere in the chain. What they did is actually master the LFE channel 10db lower on the disc. If you send the DD/DTS bitstream out digitally(optical/coax/HDMI) the receiver will automatically add the 10db boost on the LFE channel.

The problem they had was sending it out from the play over multichannel analogue connections, they couldn't add the boost in the player because then the LFE output would be above the specified limits for analogue output/input stage(10db=3x increase in amplitude).

So this is why we need to apply the 10db(15db if the player is performing Bass Management) boost at the amplifier stage

Cheers

Found this:


> When outputting a *PCM multichannel bitstream* over Denon Link, i.Link, HDMI or similar, the LFE channel will be transmitted "as-is", *and will need boosting by 10dB in the receiver. The receiver should do this automatically.* If it fails to do this before performing bass management, then you will be unable to calibrate the system correctly - *boosting the subwoofer to compensate will have the side effect of over-emphasising bass from other channels.*


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## Vader (Jul 8, 2006)

Never mind.... I just read your post again.... That is exactly what I am trying to learn... Thanks, MACCA350!

In summary, the Tosh is failing to provide the 15dB boost before BM.... c'mon, Toshiba... give us another FW update!


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## MACCA350 (Apr 25, 2006)

Vader said:


> Never mind.... I just read your post again.... That is exactly what I am trying to learn... Thanks, MACCA350!
> 
> In summary, the Tosh is failing to provide the 15dB boost before BM.... c'mon, Toshiba... give us another FW update!


I think you meant:
In summary, the Tosh is failing to provide the 15dB *cut(to the redirected bass)* before BM.... c'mon, Toshiba... give us another FW update!

Basically to mix the redirected bass into the LFE channel:

LFE channel gets cut by 5db
Redirected bass gets cut by 15db

Then they are mixed together and are now 15db below the other 5 channels. At least thats how its supposed to work:whistling:


cheers


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## Vader (Jul 8, 2006)

MACCA350,

Thanks for the correction. I think I got it, now (one of my brain cells is now in agreement with the other one). Hopefully when I am thinking straight again (I'm home with Captain Tripps - or at least that's what it feels like) I can follow this stuff a lot better...


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## Sir Terrence (Jun 8, 2006)

MACCA350 said:


> I think you meant:
> In summary, the Tosh is failing to provide the 15dB *cut(to the redirected bass)* before BM.... c'mon, Toshiba... give us another FW update!
> 
> Basically to mix the redirected bass into the LFE channel:
> ...


Actually this is a bit off. First, the LFE is uneffected by bass management. When bass is redirected from the other channels to the subwoofer, the following takes place. Each channel that is redirected is cut by 15db, and when combined with the LFE is boosted by 3db. When all channels are redirected, this results in a combined boost of +15(3db each channel x5), which restores the overall balance of all channels involved. 

When talking of LFE, each format handles the LFE quite differently. Dts is recorded with the bass set at +0 on the board. It is then to be boosted(sometimes done automatically, or set manually)+10 at the decoder level. Dolby digital on the other hand uses a -10db recording level, and is automatically boosted +10 at the decoder level. Both approaches keep the analog outputs from being overloaded, and give the 10db headroom in the LFE channels.


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## Vader (Jul 8, 2006)

Sir Terrence,

What exactly is the bug in the Tosh bass management, then? It was clear that the redirected bass from the post title sequence explosion in "The Matrix: Revolutions" was extremely hot, burying the needle on the BFD and bottoming one of my subs. It was on the TrueHD track, and I was using the analog outs (which is the only path affected by the bug).


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## MACCA350 (Apr 25, 2006)

Sir Terrence said:


> Actually this is a bit off. First, the LFE is uneffected by bass management. When bass is redirected from the other channels to the subwoofer, the following takes place. Each channel that is redirected is cut by 15db, and when combined with the LFE is boosted by 3db. When all channels are redirected, this results in a combined boost of +15(3db each channel x5), which restores the overall balance of all channels involved.


Here is what Roger Dressler(Director of Business Development for Dolby Laboratories) said about how BM is performed.



Roger Dressler said:


> The LFE signal is recorded 10dB lower than the main channels. The process of bass management usually means the bass from the main channels is mixed with the LFE, then presented to the subwoofer. The signal level in the LFE channel is permitted to reach full scale, so in order to mix anything with it, additional headroom must be provided, even when the other 5 channels are being scaled down 10dB to achieve the correct relationship relative to LFE. The amount of additional headroom provided is 5dB. The bass from the main channels is attenuated 15 dB and the LFE is attenuated 5 dB before mixing.
> 
> This means that the bass signal levels coming out of a “fixed level” player is -15dB wrt the main channels. Most AVRs are able to use this level correctly, as they apply the same "scale by -5dB" process when performing bass management internally.





Sir Terrence said:


> When talking of LFE, each format handles the LFE quite differently. Dts is recorded with the bass set at +0 on the board. It is then to be boosted(sometimes done automatically, or set manually)+10 at the decoder level. Dolby digital on the other hand uses a -10db recording level, and is automatically boosted +10 at the decoder level. Both approaches keep the analog outputs from being overloaded, and give the 10db headroom in the LFE channels.


If thats the case then how do they account for the 10db boost at the recording stage? This makes no sense, if they don't offset the LFE channel at the recording stage then the LFE will be too hot when played back on a system with the 10db boost.
I can't find anything for DTS(since DTS don't really provide whitepapers) other than this:


> LFE level adjustment
> Some receivers with integrated decoders do offer an adjustment for the LFE level - an option to NOT boost the LFE by 10dB. This is needed for some early music mixes using DTS; the studio mixers, being unaccustomed to 5.1 production, hadn't calibrated their LFE channel 10dB high. Thus the recorded LFE signal on those discs is at equal level with the other channels, and doesn't require boosting.
> 
> The unboosted LFE option on the receiver is often called "LFE -10dB", with the standard boosted option being "LFE 0dB". Alternatively the options might be called "LFE 0dB" and "LFE +10dB". Whatever, the higher option is correct for films and almost all DD and DTS multichannel music. Since those early errors, both Dolby and DTS have specifed that LFE in music releases should be mixed for a 10dB LFE boost to match film soundtracks. However, SACD still differs... more on this below.


cheers


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## Sir Terrence (Jun 8, 2006)

MACCA350 said:


> Here is what Roger Dressler(Director of Business Development for Dolby Laboratories) said about how BM is performed.


This is correct information. When I re-read the industry standards for BM, I found that I was incorrect in the cut of the LFE, but actually right on all the rest. I don't use bass management in my system except for the surrounds when I play them back at high levels. Otherwise I don't use it at all, the less processing of the signal the less degredation. 






> If thats the case then how do they account for the 10db boost at the recording stage? This makes no sense, if they don't offset the LFE channel at the recording stage then the LFE will be too hot when played back on a system with the 10db boost.
> I can't find anything for DTS(since DTS don't really provide whitepapers) other than this:
> 
> 
> cheers


Initially the Dts spec released didn't include a +10 boost at the recording level, and I should have said that before I pointed out the differences between DD and Dts LFE setups in the studio. Dts specified a +0 setting for the LFE at recording, to be boosted at the decoding stage. That is where the intial boost used to occur. This is why some receivers has options for both +0 Dts, and +10 Dts. The +10 was required to account for the non boost at the board and a 0+ setting. Once the standards were amended to make sure that all processes become standard regardless of format, then the +0 Dts was introduced as both Dts and DD were using -10 at the board. What started off in the beginning wasn't what is it now. For instance, my processor still uses the +10 setting for Dts LFE. And that is even after the standards correction. I am sure that my processor isn't the only one to do this. 

The process of dealing with BM and surround levels used to be a mess at the studio level, hence the confusion of how its done. Dolby had one level, Dts used another. I'm thankful for standards that are adapted industry wide to make this whole process and little easier to implement at both studio and receiver level.


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