Over-kill bit rate for AC3?

[j1d10t]

I've got an audio file that is PCM (stereo), and I'd like to convert it to AC3 (to save space) but was wondering what a good bit rate would be to do this. What is the best bit rate for AC3 that would sound like the original PCM file? Would it be 224k? 256k? 320k? I don't want to go overboard, and give it a really high bit rate, when a lower bit rate would do the job. Any help/input would be appreciated

[mkelley]

224 is just fine for AC3 2.0 (5.1 requires higher sampling as a general rule: usually around 384).

[j1d10t]

Cool. I was hoping I owuldn't have to go too high for the bit rate.

Thanks

[flaninacupboard]

if you want it to actually sound the same, look up monkey audio and flak audio on google. these amongst many others will perform lossless compression of about 4:1 on WAV sources, and offer realtime playback.
Unless of course you're using this soundtrack on a DVD (which you may be, but you didn't say!) in which case .ac3 256kbps is fine.

[j1d10t]

Yeah, I will be using this for DVD audio. Sorry - I forgot to mention that

[dcsos]

AS FAR AS I KNOW

224=near cd quality or usually also encoded at "44,100"
381=dvd quality or usually encoded at "48,000"
441= the only DVD I'VE SEEN WITH THIS BIT RATE IS A BOLLYWOOD TITLE NOT AVAILABLE in the STATES but Purchaseable in REGION 1 encoding (go figgure!) called "HUM TUM HARE"

even the new LED ZEP 2 DVD set is encoded at 381
(SOUNDS AWESUM)

[j1d10t]

But were those for stereo, or 5.1? I've only got stereo.

[mkelley]

224 is *more* than adequate for 2.0 AC3 -- I've never seen a commercial 2.0 AC3 disk using greater than this rate (BTW, you can check your own rates using either software or the new features found in many of the higher end players).

384 is typical of most 5.1 -- I've never heard of 381 so I suspect that poster just misstyped. Indeed, I've never seen a commercial disk using 5.1 AC3 any higher than this.

I *have* seen commercial DVDs using 2.0 encoded at 192, but these were mostly TV shows (like the Rumpole disks). I suspect even this would be adequate for most people, but I've always used 224 as it's slightly more compatible with the software I use to author.

[j1d10t]

I use 192k for my SVCDs, but they have MP2 audio (and sometimes they sound a little tinny), so I wasn't sure, and I wasn't sure how high I should go with the bit rate for good AC3 audio.

[Romper]

Baise Moi (R1) used 256 for 2 channel audio, only saw it cause it was not easiest movie to get to see in the cinemas down under.

I love it when they ban (or try to) a movie, only drives more people to want to see it.........but I digress, didn't like the flick anyway.

[txpharoah]

Most stereo AC3 commercially-made discs have 192k 48hz AC3. Fewer have 224k. You usually find this on tv series discs and cartoon discs. Most movies comes 5.1, so bitrate is higher, using 384k or greater.

[Diggedy]

First of all it needs to be said that there is some misinformation in this thread...

224 is *more* than adequate for 2.0 AC3 -- I've never seen a commercial 2.0 AC3 disk using greater than this rate

It's readily apparent that by comparing a PCM against a 224 or 192 2.0 that the 2.0 sounds AWFUL by comparison. If you want it to sound close to the PCM go for at least 256 if not higher.

384 is typical of most 5.1 -- I've never heard of 381 so I suspect that poster just misstyped. Indeed, I've never seen a commercial disk using 5.1 AC3 any higher than this.

384 used to be the standard rate, but most dvds these days (unless it's from Warner) use 448kbps for DD5.1

224=near cd quality or usually also encoded at "44,100"

No audio track on dvd can be at 44100khz... it must be 48000.

[dcsos]

YOU'RE RIGHT MKELLY
I meant to type 384 in those postings....

but this INDIAN MOVIE with 441 you gotta hear this..This INDIAN GUY thinks he's the new MICHAEL JACKSON and 441
is an appropiate rate as the musical numers in "HUM TUM HARE" are elaborate to say the least!

I wonder is this is typical of BOLLYWOOD fare?

Alo thanks..I know you can't put 44,100 on a DVD but meant to point out that 224 is the perfect choice for anything that gets transcoded from this bitrate..as HIGHT is not gaining anything..
THANKS FOR THE SPEC CLARIFICATION!!!

[Diggedy]

dcsos the bitrate you're referring to is 448kbps, 441 is not a legal DD bitrate.

[flaninacupboard]

My copy of NIN Live and all that could have been has DTS at 1.44mbps (nice!!) and DD 2.0 at i believe 448kbps. both sound very nice, but aren't a patch on the CD

[mkelley]

First of all it needs to be said that there is some misinformation in this thread...

224 is *more* than adequate for 2.0 AC3 -- I've never seen a commercial 2.0 AC3 disk using greater than this rate

It's readily apparent that by comparing a PCM against a 224 or 192 2.0 that the 2.0 sounds AWFUL by comparison. If you want it to sound close to the PCM go for at least 256 if not higher.

No, this is very wrong -- I don't know how you are encoding (that can make a difference) but it is "readily apparent" that 224 is indistinguisable from the PCM in any DVD player as listened to on the DVD itself (no other test is significant).

Perhaps you're thinking about MP3 compression, or perhaps you're using an inferior encoder. Or perhaps you're trying to compare it by listening on the computer.

In any case, I think the original poster has *more* than enough information now to make up his mind.

[j1d10t]

Thanks everyone for the feedback. I think I'll start at 224k, burn it to a DVD+RW, try it in my DVD player and see how it sounds, then go from there. Thanks again

[Diggedy]

No, this is very wrong -- I don't know how you are encoding (that can make a difference) but it is "readily apparent" that 224 is indistinguisable from the PCM in any DVD player as listened to on the DVD itself (no other test is significant).

That's exactly how I've tested it... and nothing is wrong with the encoder I'm using (Scenarist ac3enc). It also depends how revealing your speakers are... maybe your system isn't resolving all the details. I'm using full range speakers for my listening tests.

[mkelley]

Well, my particular audio system is one we use for broadcast -- so I suspect it's at least as good as yours. But that's okay -- I'm sure you know better than the studios.

[mkelley]

Ah, that's probably not fair -- I'm feeling particularly old and cranky tonight (and my kidney problems are acting up again. Sigh).

I'll let the original poster decide, as (as I said once before) he has more than enough information from all sides to make up his mind. I'll leave this thread alone for good (and go to bed :>)