Axiom Home Page Forums General Discussion Home Theater Calibration / Avia test disk

Either this new receiver I got(HK 745) has outsmarted me or it's not working correctly. I'm betting it's got me outsmarted. I've been messing around with it for several days now, well, for about as long as my patience will allow. I've read the instructions over and over and even consulted tech support. Now I'm asking for a broader opinion.

It all started when I heard how great HD/DVD's sound if you send an HDMI equipped receiver a L-PCM audio stream. And for clarification, I have the Toshiba HD-AX1 and have installed the 2.0 firmware update, so the X1 'should' be working correctly according to the gazzilion posts at the HD DVD forum at AVS.

So I select PCM with the X1 and give it a whirl. Everything sounds clearer, and the surround speakers come to life. Then I notice that there is no center channel. HU?? I go into the HK's menu and start messing with my settings. IE: channels, X-overs, delays, etc.....no matter what I do, I can't get the center channel to work when PCM is selected. Even though the HK's display shows PCM / 96 hz / Dolby PLIIx, I just don't have a center channel.

I called HK tech support again and they tell me to use the EZ EQ settings. I don't' know what good that would do, but I try it anyway. No luck, still no center channel with PCM selected.

I call Toshiba and they tell me if I select PCM, all I get is two channels. I read the Toshiba instructions and they clearly state that with True Dolby or Dolby plus, PCM, there is multi channel. So Toshiba tech is full of it.... so much for their help.

Thinking this might just be the Toshiba's fault, I pull out the Avia test disk. Still no luck with the center channel. So then I try the Avia test disk with my Oppo 970 and select PCM output. Not only do I not have a center channel, but All I have is the mains.

For clarification, when I select bitstream from the Toshiba or Raw on the Oppo, I do have all channels. Same thing if I run six channel analogue.

Are there any of you with HDMI that has messed around with PMC had similar problems?

So now that I've given up on getting PCM to work, out of curiosity I run the Avia disk again through both players to do some tweaking with the sub / LFE channel. When the test tone cycles back and forth between each speaker and the sub, the LFE channel is there for the mains, but about 15 db's lower than all other channels. This is with both players. When I ran this test with my last two HK's, the LFE test tone was balanced between each speaker and the sub.

No matter what I do to the LFE set up by selecting R/L + sub or just LFE, or the channels or the X-overs has any effect on this. It is as if there isn't any LFE for any channel but the mains.

Has anyone else ran this LFE test with the Avia calibration DVD? If so, can you tell me if you have an LFE presence with all the speakers or if it's just the mains?

:::WARNING::: I could be totally off-base here and/or talking out of my a$$ but, i have been researching the pioneer vsx84tsi receiver and have seen a lot of mention of an LFE bug on hdmi where there is difference of about 10db. i have seen it in reference to tosh hd dvd players as well as ps3 and on multiple receivers yammie 2700 yours and the pio. try avsforum for further clarification.

I believe you are correct. There is a bug. Unfortunately, that does not seam to be my problem or I would only see it with the Toshiba and not both players. I also pulled out the Oppo 971 and tried it. As expected, same problems.

I asked about PCM at another forum and a pretty sharp feller broke it down for me in a manner even I can understand.

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"PCM is the most simple way of digitising sound. It's what CD players use, it's what PCs use, it's what everything digital uses (except SACD). It works by measuring the position of the speaker/microphone thousands of times a second, and storing that position to a certain accuracy. On a CD sound is sampled 44100 times a second to an accuracy of 16 bits.

On a CD, this data is stored raw - 44100 16-bit samples a second. That means 44100*16=705.6kbits per second. Then times two because it's storing two channels for stereo: 1.4Mb/s.

Raw uncompressed PCM for a 5.1 channel film would be pretty bulky: 48000*16*5= 3.8Mb/s, plus a bit for the LFE. No way could you fit that onto a 35mm film print. And it would be rather a lot on a DVD too. Hence Dolby Digital, et al.

Dolby Digital, DTS, and all these other formats are just different ways of compressing PCM to take up less space on the disc or film print. Dolby Digital, DTS, MP3, AAC etc do this by throwing away information they think you can't hear.

Dolby Digital can squeeze 5.1 sound down to 0.4Mb/s or so - a factor of ten less space than raw PCM. The decoder takes the Dolby Digital compressed bitstream, and turns it back into raw PCM. It won't be exactly the same as it started with, but it shouldn't sound too much worse (to human ears, at least - an alien with a different hearing system might think it sounded dreadful. But then they wouldn't be convinced by our 3-colour TV either.).

The simplest way to think of it is that Dolby Digital and DTS are "MP3 for surround sound". They get the data down to a manageable size.

Now, DVD-Audio and the new HD formats have extra space for audio. So they can store either raw PCM, or they can use a lossless compression system. (DVD-Video can actually use raw PCM, but this is rare except for some 2-channel tracks on music discs, as there's usually not enough room).

These lossless systems typically can compress PCM by a factor of up to 2 or 3. Nowhere near as small as Dolby Digital, but you lose nothing in the process - the decoder gets back the original PCM undamaged. These systems are MLP (used on DVD-Audio), Dolby TrueHD (basically MLP with a few extensions) and DTS HD Master Audio.

With these lossless systems, they are all totally equivalent in sound quality, so anyone who debates whether PCM, Dolby TrueHD or DTS HD Master Audio sound better needs their head examined. They can only differ in how much they compress, or extra facilities like better downmixing, dynamic range reduction, etc. The important point when comparing soundtracks will be what resolution they're at (48kHz/16-bit, or 96kHz/24-bit, etc).

Super Audio CD is different - it uses a totally different system from PCM, called DSD. This is hard to explain, but basically it's performing 1-bit sampling at 2.8MHz. Again, this data is bulky (2.8Mbit/s per channel) so it can be compressed losslessly, using a system called DST, which typically compresses by a factor of three. DSD has pros and cons over PCM.

Now, in a sane world, all these compression systems would be handled inside the player, and interconnects between components would just use PCM or DSD. But before HDMI and i.Link came along, there were no digital interconnects that could handle 6-channel audio. So as a fudge, the Dolby Digital and DTS bitstreams were squeezed into the 2-channel space of S/PDIF and TOSlink, and the receiver had to have decoders (as well as the player, for its analogue outputs). This fudge only worked for the highly compressed bitstreams. There's no room in S/PDIF to pull the same trick for the lossless formats.

But now we have HDMI and i.Link, with their support for multiple channels of hi-res PCM/DSD, there's no need to send a bitstream across them. The player can do the decode, and the receiver can just accept raw PCM or DSD."

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That was extremely informative for me. Thanks Mdrew

(Should I be scared for myself that I've only been hanging out here a month and that actually was interesting???)

Great info Mike. It only seems to make sense to me that your receiver doesn't fully understand the PCM it is getting over the HDMI. Could this be an HDMI version incompatibility with the receiver and the player? Seems like you had to have 1.1 for multichannel PCM audio to work? I can't remember, sorry. I think it would be worth checking into or trying a different HDMI receiver, even though your HK 745 should be new and up to the task. Maybe take your disc to some store displays with different recievers and see how they behave.

The last reply I got from HK tech support was "this may be in the receiver, our engineers are looking into it".

I'm beginning to feel like an unpaid beta tester. The 745 does have HDMI 1.1 and "should" support multi channel PCM.

I just think I've got another HK lemon. I'll wait and see what they offer me as a solution. In the meantime, as suggested by HK tech, I'm running the six channel analogue cables. This 745 has a neat feature not available in other models/brands of receivers. It has a six channel DVD audio selection that I can select any of the surround formats with including PLIIx or DTS + PLIIx. It also allows me to adjust the channels at will. pretty cool.....Sounds great too!

Ah mdrew, the bugs just never end eh?