AC3 audio data rate question

[Keithchr]

Hi, below are the setting for creating a video file from my movie making software. My question relates to the AC3 audio data rate. The AC3 plugin I have converts the DV footage LPCM to ac3 audio at a rate of 224 kbps. Is this OK...would I gain anything by setting the rate higher to say 256 etc? Obviously, when I am creating a video file containing some MP3s or WAVS the data rate varies on these - should this have any bearing on the setting I should use or is 224 fine? Thanks for your time.

MPEG files
24 Bits, 720 x 576, 25 fps
Lower Field First
(DVD-PAL), 4:3
Video data rate: Variable (Max. 8000 kbps)
Audio data rate: 224 kbps
AC-3 Audio, 48 KHz, 2/0(L,R)

[yoda313]

Hello,

Well I would think 224 should be ok. Have you tested it yet???

Just a note on real dvds most documentaries are at 192 or lower. That should be a good benchmark for you (most are that low so they can fit more video on the bonus disc by using a lower audio bitrate - after all it's just a bunch of people talking ).

Good luck.

Kevin

[Capmaster]

Hi, below are the setting for creating a video file from my movie making software. My question relates to the AC3 audio data rate. The AC3 plugin I have converts the DV footage LPCM to ac3 audio at a rate of 224 kbps. Is this OK...would I gain anything by setting the rate higher to say 256 etc? Obviously, when I am creating a video file containing some MP3s or WAVS the data rate varies on these - should this have any bearing on the setting I should use or is 224 fine? Thanks for your time.

MPEG files
24 Bits, 720 x 576, 25 fps
Lower Field First
(DVD-PAL), 4:3
Video data rate: Variable (Max. 8000 kbps)
Audio data rate: 224 kbps
AC-3 Audio, 48 KHz, 2/0(L,R)

224 is the typical audio bitrate for DVD. With 48 KHz and 224 Kbps, it's better than CD audio. You'll never hear the difference by bumping it up, but you'll see the audio track get larger. Stick with 224

[BJ_M]

not better than cd audio - which though 44.1 khz sample rate, it IS uncompressed ,

[Capmaster]

not better than cd audio - which though 44.1 khz sample rate, it IS uncompressed ,

Oops - you're right. I was thinking of the original DVD NTSC standard LPCM audio, which is uncompressed. My bad.

[freestyler]

224 is the typical audio bitrate for DVD.

For stereo content, dolby has always recommended 192

[Capmaster]

224 is the typical audio bitrate for DVD.

For stereo content, dolby has always recommended 192

That is correct:

Dolby Digital is multi-channel digital audio, using lossy AC-3 coding technology from PCM source with a sample rate of 48 kHz at up to 24 bits. The bitrate is 64 kbps to 448 kbps, with 384 or 448 being the normal rate for 5.1 channels and 192 being the typical rate for stereo (with or without surround encoding).

And for MPEG audio, 384 is the normal rate:

MPEG audio is multi-channel digital audio, using lossy compression from original PCM format with sample rate of 48 kHz at 16 or 20 bits. Both MPEG-1 and MPEG-2 formats are supported. The variable bit rate is 32 kbps to 912 kbps, with 384 being the normal average rate

The early LPCM spec which was mandatory for NTSC DVD compatibility on the first-gen players, 224 was the standard bitrate for DVD audio. I still use this bitrate, as many others do, for MP2 audio.