Player decoding or Receiver decoding, that is the question

[welwynnick]

Secondly, I believe there are some ways in which I can give you some more confidence about my observations (besides getting you to come round and hear for yourself).

To begin with, I tried playing a BD that had an LPCM sound track - Happy Feet (I was just after something with some music on it). To my embarassment, I thought it had a Dolby TrueHD soundtrack, and proceeded to compare decoded and bitstream output. This is what I said about it on Jan 26:

I think what I found with amplifier decoding is easiest to summarise first. This is what I was really keen to hear for myself, never having had the opportunity before. Every time I made the comparison, I fancy that LPCM sounded better, but the difference was so small that I doubt I could tell the difference reliably. LPCM seemed to have a bit more sparkle and transparency, which is the opposite of what I was expecting of course. There were much bigger differences elsewhere, and if my player or amp constrained me to using one or the other, it really wouldn't be a factor.

And then this:

There's been a lot of attention on bitstreaming, and I appreciate the reasons and benefits and would be the first to promote it. Some players don't decode DTS MA, and some amps like the 8000AP don't decode any HD audio. My view is that as long as it's done somewhere, I shan't worry. Of course, it could be that other amps and processors deal with bitsream differently to Onkyo, or have a different sensitivity to LPCM jitter. What HiFi criticised the 8000Ap for not having HBR decoding, but my view is that the quality of the D to A conversion is an order of magnitude more important than where the decompression is done.

So without realising my mistake, I correctly called PCM & BS as indistinguishable, and was somewhat disappointed. Effectively, I threw myself a control test without realising it, and passed. Some time later, I realised my mistake and used a BD with TrueHD instead. Having gone into print, I had to make a slightly embarassed retraction:

Oooops!

I think I may have spoken too soon and covered myself in embarassment.

I was listening to some of the musical sections on Happy Feet, and switching between LPCM and native to compare the effect of bitstreaming. In the back of my mind I had this idea that HF was a DTHD BD - but its not, and that may explain why I didn't hear a difference. Of course, there might not be a difference anyway, but I simply had to try again tonight.

This time I played the first chapter of National Treasure Book of Secrets, which is DTHD; 48kHz, 24 bit, no less. I played this over LPCM from the 3800 to the 886, then over bitstream. Then I played it over LPCM from the BH200 to the 886, then over bitstream.
Well - what happened. Did I hear a difference?

Seriously, it was like listening to a different soundtrack. All the sounds were there, the frequencies and the dynamics and everything, but with LPCM the 886 was seemingly throwing all these high resolution sounds at you without making sense or order out of them. It was like a string of events, rather than a creative situation. The Lexicon seemed to know how to organise the music it was reproducing and make it convincing, even if it didn't have HBR capability.

With bitstream into the 886, though, everything seemed to come to life. The sounds were the same, but it was like it was happening in front of you, instead of being an accurate reproduction. A wall of sound became a room full of tangiable sources. This has only happened in the last few minutes, so I want to go back and check. Again. And again. Just to be sure.

I guess I could be deluding myself, but I don't think theres any question about it to my mind, its hardly difficult to spot. I had already come away with what I thought was a null result, and I was happy just to have the answer that I wanted. It wouldn't have stopped my getting an amp or processor with HBR decoding, I just wouldn't have cared so much. Now I do, but I'm going to check for sure.

This is an absolute revelation, and the 886 is sounding mighty fine. In subective terms its up with the better stereo systems that I remember so fondly, its that good. Its left any DD/DTS based system behind in my opinion. My goodness, I've got to go and listen to allmy BDs again. heck, why did I bother buying all those cheap HD DVDs with their infernal dolby digital plus soundtracks? Damn. This is the most exciting day I've had for -er- yonks.

In a previous post I thought I wasn't yet hearing everything that was on the disc. Well, I think I made a big step in that direction. I have no doubt that I could spot this reliably with blind testing, and will see if I can sort something out.

I then got my wife to listen to various soundtracks, without telling here what she was listening to (I think she's like yours...):

I'll probably finish off my contribution to player decoding by describing a session I had with my wife last night. I did type it up afterwards, but lost it to finger trouble, so I'll try again now. No, you misunderstand - we were just watching Blu-rays, only this time I persuaded her to do some blind listening for me. Being rather less enthusiastic about AV than I am I thought she might be more independant, and contribute some lateral observations. We watched the first chapter of the following films, which all had 24 bit soundtracks:

1. National Treasure 2; True HD
2. The Golden Compass; DTS MA
3. The Day After Tomorrow; DTS MA
4. Blade Runner The Final Cut; True HD

These were played through both the LG BH200 and Denon 3800 BDCI to the Onkyo SC886, and we compared decoded and bitstream feeds. Obviously the DTS MA tracks had to be decoded on the Denon. I didn't tell my wife what we were listening for, or what to expect, or even whether there ought to be a difference. I switched the formats in a random order to avoid the natural preference for the second sample.

To my pleasant surprise, not only did she find that there was a difference, but also that she preferred the bitstream replay every time, at least to begin with, before getting tired. She described it as clearer, better in the treble, easier to hear dialogue, and more realistic. However, after a while she got tired of my demands and lost some listening power. We tried going backwards and forwards several times with each film, got confused, then called it a night. Its not easy.

One thing we did notice that time, though. The difference between LPCM and bitstream was greater with the LG BH200 than the Denon 3800BDCI, so the latter was giving a higher quality LPCM output. I got the overall ranking:

90% Bitstream from Denon
90% Bitstream from LG
85% LPCM from Denon
80% LPCM from LG

and concluded that a pattern is emerging:

IF: your player puts out lots of jitter on the LPCM output over HDMI,
AND: your amplifier is susceptible to jitter on these imputs,
AND: your amplifier doesn't use LPCM video clock recovery for audio clock regeneration with bistream inputs,
THEN: your system will sound better with amplifier decoding of compressed audio.