LCPM or Dolby digital audio, which is best?

[jparnold]

I recently created a "make movie template" for creating a DVD movie and for unknown reasons chose MPEG as the audio format (under the compression tab). I also chose 9570 kbit/s as the video data rate as this appears to be the maximum it should be set to and I wanted the highest quality possible (my 'movie' is 28 minutes so easily fits a single layer DVD).
I then created a DVD and watched it on my TV.
I quickly noticed that the sound appeared to be "scratchy" (not much base and lots of treble).

I then checked the settings for the "standard" PAL DVD movie template and noted that the audio format was set to LPCM (remember I had used MPEG).

I have checked some posts here regarding audio format including Steve's excellent explanation stating that LCPM used a lot of 'space' (which I don't care).

Is it 'normal' for MPEG formatted sound to be "scratchy"?
Should I stick with LCPM? What are the 'cons' using Dolby digital?

[Ken Berry]

LPCM is the absolute central, rock standard, central (you get my drift?) format for DVDs. Both NTSC and PAL have it as their sine qua nons. It is high quality and excellent, and ALL DVD players in the world are required to be able to play it as it is the central audio element of both the NTSC and PAL international DVD standards. The only downside is, as you know, the fact that LPCM files are relatively large.

After that, PAL can play both Dolby and mpeg layer 2 audio. Both are not too dissimilar to each other, though they use different algorithms to produce themselves. They are both capable of high quality but because they are compressed, produce smaller files. The international PAL DVD standard recognises both as valid audio formats. However, the NTSC DVD standard only recognises Dolby as a legitimate alternative to LPCM. In other words, NTSC players are not required to be able to play back mpeg layer 2 audio, though in practice these days, most do.

As for your specific question, without knowing the specific compression you have applied, I cannot really answer. But like any compressed format of either video or audio, the more compression you apply, the more the potential loss of quality. Or conversely, just like video, the higher the audio bitrate you use, then the better the quality. So if your mpeg layer 2 audio had a setting which used a low bitrate, that could account for the lower quality. Increase it, say, to 196 kbps or even 256 (which is what I normally use) if it is 128 or lower.

There is no downside, as far as I am aware, to using Dolby, though again, to maintain high quality, you need to use a higher bitrate.

[GuyL]

I've used all three and my ear can't tell the difference. I'm sure an audiofile can and would cringe at me saying so. I"m just reporting my experiences.

[jparnold]

Thanks for your input.

Quite by accident I think that I have found the culprit (why my latest DVD movie sounds tinny).

I noticed tonight that the sound from my plasma watching TV channels also sounded a little tinny but not quite as much as my DVD movie created.

I checked the audio setting on my plasma and found that someone had set the treble on FULL and set the bass down. So problem solved (I think).

[DVDDoug]

When I've converted from MPEG audio (the only format I can get from my capture card) to Dolby, I've noticed some distortion. This was cured by reducing the level to 75%. (Of course, there is always some quality loss when converting from one compression format to another.)

Although LPCM is "better" than Dolby*, the only way to get 5.1 digital surround is with Dolby or DTS.


* Dolby, MPEG-2 audio, MP3, and DTS all use "lossy" compression (as does MPEG-2 video). Data is thrown-away during the compresson process. However, Dolby sounds quite good to me. Especially in 5.1 surround!

[etech6355]

Although LPCM is "better" than Dolby*, the only way to get 5.1 digital surround is with Dolby or DTS.

Just to add to this on many dvd players & highdef players you have a choice of "BitStream" or "Linear PCM". Many 5.1 receivers only work with the PCM. When you use the PCM setting in you dvd player the audio files are converted back to raw lpcm audio and sent to the audio amp via optical or coax connection.
A "BitStream" setting leaves the audio at it's encoded compressed bitrate.