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Author Topic: 7.1 PCM issues vs. Bitstream.  (Read 3998 times)

Sandy B Ridge

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7.1 PCM issues vs. Bitstream.
« on: July 25, 2011, 10:49:50 am »

I have started to decode and send 7.1 PCM to my receiver rather than bitstream as I used to. I downloaded some DTS MA, TrueHD and PCM channnel test files (all 7.1) to test whether my amp was set up correctly.

My lounge isn't very large and so I don't have room for the surround back speakers( sofa backs onto a wall), so I have the surround speakers at about 100 degrees to the TV in a 5.1 configuration. I then use the extra 2 amp channels to biamp the front 2 speakers (I thought this improved the sound quality from the speakers when I did the initial testing when setting up the system, running cable etc).

When bitstreaming the SBR and SBL channels are correctly matrixed to the rears, and actually sound more rear than the SR and SL channels bizarrely, although that may be placebo effect! However when decoding and sending 7.1 PCM to the amp (says 7.1 PCM on the display) the SBR and SBL channels are silent. :-( this is for the decoded DTS MA, TrueHD and the native 7.1pcm files.

I assume it is an Amp issue (Arcam AVR600) as they are noted to be a bit buggy, but sound sublime! Anyone else have similar issues with 7.1 tracks?

I suspect it won't be a major issue as there are very few discs with 7.1 tracks out there at the moment, but annoying none the less. 

SBR
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Matt

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Re: 7.1 PCM issues vs. Bitstream.
« Reply #1 on: July 25, 2011, 10:57:21 am »

Are you using the 'Parametric Equalizer' in DSP Studio to handle bi-amping?  I'm doing something similar to this, but with a subwoofer.

You would put 'Parametric Equalizer' last in DSP Studio and have it copy the L / R to the RL / RR channels.  Then hook the RL / RR channels into your bi-amped mains.  You could also use the Parametric Equalizer to handle the cross-over, since it can almost certainly do a better job than the amp or hardware cross-over.

You can use Room Correction to test once everything is configured to make sure you have the right channels going to the right places.

Are you at the point where Room Correction can talk to each speaker correctly?
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Matt Ashland, JRiver Media Center

Sandy B Ridge

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Re: 7.1 PCM issues vs. Bitstream.
« Reply #2 on: July 25, 2011, 02:26:34 pm »

Are you using the 'Parametric Equalizer' in DSP Studio to handle bi-amping?  I'm doing something similar to this, but with a subwoofer.

You would put 'Parametric Equalizer' last in DSP Studio and have it copy the L / R to the RL / RR channels.  Then hook the RL / RR channels into your bi-amped mains.  You could also use the Parametric Equalizer to handle the cross-over, since it can almost certainly do a better job than the amp or hardware cross-over.

You can use Room Correction to test once everything is configured to make sure you have the right channels going to the right places.

Are you at the point where Room Correction can talk to each speaker correctly?

Thanks Matt,

I was hoping to get the amp to do the grunt (it's expensive enough so should be able to!). It seems to do a perfect job of matrixing the 7.1 down to 5.1 with bitstreamed data from 7.1 TrueHD and DTSMA. So I do not understand why it doesn't do the same for uncompressed 7.1 PCM! I have DSP Studio off at the moment apart from the necessary for Videoclock (the main reason for me now wanting to decode and send PCM because of the Intel 23p problems). I have the amp do room correction at the moment - it has an semi auto setup to do this with a supplied mic. I'll certainly give DSP Studio a go. I guess there's no harm in doing room correction twice! I think I would rather be able to use it for video, but leave audio as a 'pristine' stream (I have my CD's ripped to uncompressed wav and would like to send 'bitperfect' audio at least). Is it possible to configure this way?

Also if I use DSP Studio configured for 5.1 with channel copy, am I limited to always converting 2.0 audio into 5.1 also?

I may post on some Arcam forums too to see if anyone else has any issues. I'm just not registered on any at the moment.

As I posted on the subtitle thread, my chances for lengthy fettling with the kit is limited at the moment with new Baby Ridge on the scene!

Cheers,

SBR
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Matt

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Re: 7.1 PCM issues vs. Bitstream.
« Reply #3 on: July 25, 2011, 02:38:46 pm »

I was hoping to get the amp to do the grunt (it's expensive enough so should be able to!). It seems to do a perfect job of matrixing the 7.1 down to 5.1 with bitstreamed data from 7.1 TrueHD and DTSMA.

I wouldn't expect the amp to handle bi-amping?

If it does, you would want to output 5.1 from the computer and let the amp split the L/R channel for bi-amping.

But I'm not sure this would be better than just using the computer for everything.



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I guess there's no harm in doing room correction twice!

I wouldn't recommend this as a permanent solution.  You only want one phase adjustment for distance, and it should be one of the last things in the chain.



Quote
I think I would rather be able to use it for video, but leave audio as a 'pristine' stream (I have my CD's ripped to uncompressed wav and would like to send 'bitperfect' audio at least). Is it possible to configure this way?

You can DSP Studio > Output Format to output 2.1 from a 2.0 source.

You can also create multiple zones with discrete settings.

But things like levels and speaker distance should be used for audio and video.  There's no argument that it's more pristine to have the left speaker sound louder than the right speaker, or be out of phase due to placement.



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As I posted on the subtitle thread, my chances for lengthy fettling with the kit is limited at the moment with new Baby Ridge on the scene!

Congratulations!  My experience is that the first year is a little rough, then they just keep getting more fun.
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Matt Ashland, JRiver Media Center

Sandy B Ridge

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Re: 7.1 PCM issues vs. Bitstream.
« Reply #4 on: July 26, 2011, 10:50:44 am »

I wouldn't expect the amp to handle bi-amping?
 

The amp has a 'use channels 6 & 7 to biamp fronts' option which I'm using, so the amp's circuitry is doing this processing.

Quote

I wouldn't recommend this as a permanent solution.  You only want one phase adjustment for distance, and it should be one of the last things in the chain.


Yes of course, double the processing has the potential for double the problems. So I'll try and avoid this. As the amp has supposedly quite advanced room correction algorithm, I would probably want to leave this for the amp to do as the last step in the chain.

Quote

You can DSP Studio > Output Format to output 2.1 from a 2.0 source.

You can also create multiple zones with discrete settings.


Great idea, but not sure about the WAF for this. Would have to be a set it and forget it method for both audio and video!

Quote

Congratulations!  My experience is that the first year is a little rough, then they just keep getting more fun.

Cheers mate!

SBR
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