AC-3 or PCM Audio?

Kimberly schrieb am 12.07.2013 um 16:55 Uhr
Hello All:

VP12 Build 563.

I searched the Forum to see if I'd asked this question in prior years . . . not sure that I or others have, or maybe my search skills have become rusty in the six months that I've been overseas!

AC-3 or PCM audio -- is one better than the other for output on DVD or BD? I've always used AC-3 Stereo at 48,000hz and it has always worked fine on DVDs. I'm focusing now on BDs so thought I would ask.

Note: I am not an audiophile nor are my disks intended for use by audiophiles.

Regards,

Kimberly

Kommentare

craftech schrieb am 12.07.2013 um 17:08 Uhr
Kim,

Is the sound track music or singing? My preference for that is PCM, but usually space requirements prohibit it.

On a BD you can use 448 KB/s AC3 which sounds very good, but again what is the nature of the sound track?

John
Kimberly schrieb am 12.07.2013 um 17:17 Uhr
Excellent question.

It's instrumental music, no voice. I mute all native audio and just have music. I use mostly "New Age" style music from SmartSound with strings, guitar, piano, and synths depending on the piece.

I've been rendering my current AC-3 audio for DVDs to top out at about -13db on the Vegas mixing console. (I know almost nothing about audio other than it is a discipline as vast as video.)

The DVDs and BDs will run about 30-35 minutes total to give you a idea of how big they are. I'm new to BD so I will play around with the bitrates. The footage is mostly 1920 x 1080 24p.

Regards,

Kimberly
videoITguy schrieb am 12.07.2013 um 17:18 Uhr
My preference is always PCM audio - but it can cause havoc with your bit-rate budget if you are maxing out volume size on a DVD. That is why most people will say AC-3 is good enough.

Still my pref is PCM audio for quality and max bang for the buck. It can make a good deal of difference if you have an excellent master soundtrack authored by you or contractual entity for you.

My Blu-ray output is max quality on the video and so I do not choose to compromise with AC-3 for the audio. You are also unlikely to run out of volume space on a Blu-ray media burn.
robwood schrieb am 12.07.2013 um 18:28 Uhr
AC3 is good enough. Just don't set the data rate too low. Target high-end around 384/448 for DVD. 448/640 for BD. I use lower settings for both (256/384 max).

If you're running stereo, PCM should be fine. But I've had 5.1 PCM audio cause a "pop" at the end of each track on a DVD playlist, this went away when same files were encoded to AC3.
larry-peter schrieb am 12.07.2013 um 19:06 Uhr
You're fine with high bit AC3 quality-wise, but I've had clients who wanted to play back from computer and there are, at least in my area, many who don't have AC3 codecs installed and get no audio playback with the video. So in any case where space/quality allows, I'll use PCM as primary audio track and add a secondary AC3 track.
craftech schrieb am 12.07.2013 um 20:21 Uhr
The DVDs and BDs will run about 30-35 minutes total to give you a idea of how big they are
==============
Then space on the DVDs to fit PCM audio is probably not a problem. On the BDs it certainly is not.

In terms of using very high AC3 bitrates on a DVD as someone suggested, I would advise against it especially if the DVDs are for distribution to customers.

Many DVD players cannot handle very high audio bitrates and can cause freezes, hickups, or refuse to load at all. All of them will handle PCM.

John

musicvid10 schrieb am 12.07.2013 um 21:11 Uhr
If I had plenty of space on my disc, and there is a high quality music program, PCM "might" be tempting.

If I was in a situation where using PCM would require lowering the video bitrate to fit on a full disc (as mine usually are), I would always opt for good quality AC3.
vtxrocketeer schrieb am 12.07.2013 um 21:28 Uhr
My paid work is choral and instrument concert recordings, so pristine audio is a non-negotiable. Period.

For Blu-ray, I always choose 96 kHz / 24 bit PCM. For DVD I use 448 kbps AC-3 on the rare occasion when space is an issue, otherwise it's 48 kHz / 24 bit PCM. Never had a problem with any of these combinations.

A client who plays any of my discs on a laptop likely won't care about (or even notice!) the audio quality, but someone who plays a disc through a home theater system should definitely appreciate my attention to audio detail and quality.
Kimberly schrieb am 12.07.2013 um 21:58 Uhr
My paid work is choral and instrument concert recordings, so pristine audio is a non-negotiable. Period.

Makes perfect sense in that setting : )

As some of you may already know, my paid work consists of a weekly trip video for my scuba diving guests. My guests are most interested in seeing themselves and the cool diving stuff so I want my audio to complement the video piece.

I've never had a customer say their audio didn't work with my AC-3, but your comments have given me a better idea of how to approach my BDs (and DVDs for that matter).

Thanks a million!
musicvid10 schrieb am 12.07.2013 um 22:06 Uhr
If I had the luxury of recording all eight subs in 96/24, I would certainly do it.
However, 48/16 will have to serve if I want everything the same.
A one-hour audio program of 5-channel surround at 96/24 PCM would take up about 2.4GB, if my math is correct. I certainly wouldn't be doing that on a DVD.
riredale schrieb am 13.07.2013 um 00:44 Uhr
My only experience is with DVD distribution.

For that short a program, you have ample space for either AC-3 or PCM.

I have never had any issue with 2-channel AC-3 at 192Kb/sec, and have never seen any objective tests where people could tell any difference.

For my DolbyDigital 2/2 (4-channel surround-sound) projects, I encode at 384Kb/sec, which of course is twice the 2-channel bitrate.

Now perhaps there are some golden ears out there who can reliably distinguish between AC-3 and PCM. But again, I've never read of any tests where people could reliably pick one over the other. Certainly for low-bitrate mp3 one can hear the differences.
vtxrocketeer schrieb am 13.07.2013 um 06:08 Uhr
My guests are most interested in seeing themselves . . .

Ya know, for most of my family/fun videos and to a lesser extent my school concerts, that is pretty much the rule. Put all the work to achieve pro results and at the end of the day, the rank and file get a thrill just from seeing themselves on TV. <sigh>

I usually record 8 tracks at 96/24; I can do 4 at 192/24. My other recorder, a Korg MR-1000, lays down 2-track audio at 5.6 MHz in DSD format. Yes, you read that right. Fed a signal through my Sound Devices 302, the Korg's audio is something otherworldly to behold when auditioned through studio quality cans. Ain't no one but me and maybe another discriminating pair of ears will care.

So keep producing those lovely underwater videos. They are truly enjoyable to watch.