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cpix
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Post subject: Re: ac3 question. Posted: 31 Dec 2015, 15:58 |
True fan |
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Joined: 11 May 2009, 11:12 Posts: 270 Location: Norway Has thanked: 0 time Been thanked: 0 time
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substance wrote: Analog fm signal turns into a digital bitstream signal of 384kbps. Far from pcm. Dolby uses its own codec but it's similar to aac. aye, ok, i've been trying to find a solution to downmix ac3 and/or dts to stereo, was hoping the crystalio could do it, but it only handles PCM, and found this device on ebay but not sure if it will work or not http://www.ebay.com/itm/WyreStorm-EXP-C ... SwcF9UWsEX
_________________ Pioneer KURO KRP-500M, Crystalio 2 VPS3300, Lumagen 2144, HLD-X9
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cpix
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Post subject: Re: ac3 question. Posted: 31 Dec 2015, 18:03 |
True fan |
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Joined: 11 May 2009, 11:12 Posts: 270 Location: Norway Has thanked: 0 time Been thanked: 0 time
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substance wrote: Any tv should downconvert it to stereo possible, but i want it hoked up to my amplifier
_________________ Pioneer KURO KRP-500M, Crystalio 2 VPS3300, Lumagen 2144, HLD-X9
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substance
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Post subject: Re: ac3 question. Posted: 31 Dec 2015, 19:37 |
Confirmed Padawan |
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Joined: 16 May 2009, 18:05 Posts: 3589 Location: California, USA Has thanked: 28 times Been thanked: 328 times
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Dolby Digital (AC-3) is the same codec with different bitrates on LD, DVD, and BD but it may or may not go through two different masterings methods.
In the LD days, it wasn't backwards compatible to play on 2ch systems. For that, they included the Dolby Surround encoded PCM channels for systems without AC-3 capability. It is in most cases the folded down version of the AC-3, matrixed into 2ch.
In DVD days, Dolby promised full backwards compatibility. If thr DVD has AC-3 as its only available soundtrack, the DVD player can internally fold it down to 2ch stereo. This requires the second mastering method which has a slight different mix which can be easily folded down. First of all, dynamic range and the rear channels separation are compromised. The rear channels are recorded out of phase so that when combined into 2ch, they don't sound amplified. This is one of the main reasons, AC-3 on DVD doesn't sound as good.
Now well mastered DVDs(like Criterion) use two soundtracks, one for the 5.1 mix and one for the 2ch folded down mix. These do not compromise dynamics and surrounds separation therefore should sound as good as the LDs. They are far and between unfortunately. Most studios choose the 5.1 mix that can be folded down.
After all this is said, I don't recommend folding down AC-3 on the laserdisc. It will not sound right. The mix wasn't designed to be down converted. The PCM channels offfer the down converted soundtrack in much higher fidelity anyway. There is no benefit, in fact you are compromising both the mix and fidelity. PCM channels are encoded at 1.2mbps vs AC-3 at 384kbps to remind you.
_________________ Coming Soon Derman Labs Anything Of Substance
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cpix
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Post subject: Re: ac3 question. Posted: 02 Jan 2016, 01:20 |
True fan |
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Joined: 11 May 2009, 11:12 Posts: 270 Location: Norway Has thanked: 0 time Been thanked: 0 time
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signofzeta wrote: The player itself already outputs stereo. I don't see why you want to the AC3 mix converted when you already have stereo PCM coming out the TOSLINK. people have said the ac3 might have better bass than the pcm tack, thats why
_________________ Pioneer KURO KRP-500M, Crystalio 2 VPS3300, Lumagen 2144, HLD-X9
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substance
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Post subject: Re: ac3 question. Posted: 02 Jan 2016, 01:46 |
Confirmed Padawan |
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Joined: 16 May 2009, 18:05 Posts: 3589 Location: California, USA Has thanked: 28 times Been thanked: 328 times
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The LFE track is not added to the down-mix. If you use an AV reciever, when you disable the subwoofer, all the subwoofer information is sent to fronts. This is the only you get the LFE in the downmix.
The biggest trouble with the downmix is because Dolby employs a minus 3db attenuation on the surround channels when added to the fronts. There is a good reason for this. In signal processing, when you add two in phase and identical signals, you get the same signal with double the amplitude. Minus 3db attenuation compensate this however any signal which is not in phase or identical to both channels do not get amplifed when added up. Dolby down mix applies minus 3db attenuation anyway. Due to this some signal is lost half energy.
As signofzeta suggested, use the pcm channels instead. The fidelity is much higher, doesn't suffer mixing casualties. The whole point of AC-3 was much higher channel separation than Pro logic, it was never about better sound. Matrix method allows about 10-12 db channel separation. Pro logic decoder applies steering, which increases this to up to 30db. Pro logic steering also has its major flaws like guessing the direction wrong. It's basically bunch of comperators calculating the dominant channel in the recording then applies attenuation to the other channels to increase the separation. Dolby Digital with its discreet channels allow above 45 db channel separation.
I don't know how DTS does its down mix. I didn't read its tech paper on this. I don't see it done any other way so it's probably the same method.
_________________ Coming Soon Derman Labs Anything Of Substance
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little-endian
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Post subject: Re: ac3 question. Posted: 01 May 2016, 07:36 |
Shows curiousity |
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Joined: 25 Jun 2015, 01:53 Posts: 29 Has thanked: 1 time Been thanked: 1 time
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substance wrote: Analog fm signal turns into a digital bitstream signal of 384kbps. Far from pcm. Dolby uses its own codec but it's similar to aac. No, it doesn't turn into a digital bitstream because it is digital to begin with. It doesn't matter in which form logically digital information manifest, as long as it meets the criteria to be treated digitally on a logical level, then it is. Just as VHS optionally had PCM tracks, in theory, one also could use a vinyl record digitally if there is enough error correction applied. Probably due to the very limited bandwidth and high distortion, the effective PCM audio wouldn't meet high standards though. Furthermore, the quote 384 kbps stream is what is left over when one strips the stuffed PCM data which in total runs at 1536 kbps. The bitrate of the raw S/PDIF stream is even higher of course due to the additional data. The technicial correct explanation is that you got a broadband modulated FM signal which is demodulated to a baseband signal and output as S/PDIF. Cause this is what a demodulator does: it demodulates, not converts analog into digital ones or vice versa. cpix wrote: Does it become PCM after being demodulated? This is actually not so far from the truth. As S/PDIF carries AC3 and DTS both as baseband PCM, in order to properly capture and further process it, both formats may be treated as regular 44.1/48 kHz at 16 Bit Stereo LPCM first and then extract the carried lossy audio from that.
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