Minimum suitable bitrate for 5.1 AC3 audio?

[orion44]

What would be the minimum suitable bitrate for 5.1 AC3 audio?

Is 384 kbps good enough for 5.1 AC3 audio?

[Blue_MiSfit]

It's "good enough" but it's not fully transparent. 384 Kbps will still lowpass filter a lot of stuff out.

If you're using AC3, I say spend the full 640 Kbps. If you must save some space, 448 is a good compromise, and was often used on DVD. 384 is the minimum to get decent quality.

[SeeMoreDigital]

orion44,

Is there any particular reason why you need to use AC3?

[orion44]

Originally Posted by SeeMoreDigital

orion44,

Is there any particular reason why you need to use AC3?

Lower file size.

[mariush]

Maybe consider AAC then, should give higher quality than AC3 and it should have wide support. VBR 256-320 kbps for 5.1 should give decent quality.

NeroAAC command line encoder can do 5.1 and MeGUI should support it : https://www.videohelp.com/software/Nero-AAC-Codec

If you don't care about playback on TVs (older), consider Opus ... it's new and open source and should give better quality than the standard AAC.

[SeeMoreDigital]

Originally Posted by orion44

Lower file size.

Hmmmm... What's your playback device?

[orion44]

Originally Posted by SeeMoreDigital

Hmmmm... What's your playback device?

I only use desktop PC.

[mariush]

Use Opus or AAC then...
If you have foobar2000 (music player) https://www.foobar2000.org/download you can right click on an audio file and select convert. Select Opus and choose VBR and pick your vbr bitrate...256-320 kbps for 5.1 should be perfectly acceptable.
If it asks where you have the OpusEnc executable, download the opus codec package from official website and unpack it somewhere and select the opusenc.exe file : https://archive.mozilla.org/pub/opus...2-opus-1.3.zip

[tebasuna51]

Originally Posted by orion44

I only use desktop PC.

If you have the audio Receiver/Amplifier 5.1 conected by HDMI to PC you can use Opus/AAC/EAC3 for your movies, with better quality/size than AC3.
The player in PC (MPC-HC, VLC,...) decode the audio and send PCM 5.1 by HDMI.

If you only have a SPDIF conexion between PC and Receiver you must remain use AC3 to preserve 5.1 channels. The player must send AC3 without decode because SPDIF only support decoded PCM stereo.

[SeeMoreDigital]

Originally Posted by tebasuna51

If you only have a SPDIF conexion between PC and Receiver you must remain use AC3 to preserve 5.1 channels. The player must send AC3 without decode because SPDIF only support decoded PCM stereo.

I haven't checked recently but does Media Player Classic still offer the ability to transcode multi-channel formats such as: AAC and Opus to AC3 and pass it via SPDIF or HDMI

[sneaker_ger]

MPC-BE's audio decoder has an option to encode to AC3. MPC-HC does not have this feature built-in but can be added via e.g. MPC-BE's filter, AC3filter, ReClock.

[tebasuna51]

I make a mini test encoding a 5.1 to opus, aac (qaac) and eac3 (ffmpeg) at 320 Kb/s.

For me are transparent all, but using spek, I know than frequency analysis is only a part of quality mesurement, I see some differences:

- opus cut frequencies greater than 20 KHz, qaac greater than 17 KHz and ffmpeg 16 KHz.

- maybe is not important but the opus seems more "clean" than qaac

I can't obtain a exac 320 Kb/s from qaac, from 307 jump to 340, the sizes:

Pines_5.1.wav           166.920.236
Pines_5.1.wav_340.aac     8.292.039
Pines_5.1.wav_320.ac3     7.728.640
Pines_5.1.wav_320.eac3    7.728.640
Pines_5.1.wav_320.opus    7.539.904
Pines_5.1.wav_307.aac     7.488.531

The 307.aac is near 320.opus in size because the real bitrate for the opus file is 312 Kb/s

See the image: source, opus, aac

[chros]

Originally Posted by tebasuna51

I make a mini test encoding a 5.1 to opus, aac (qaac) and eac3 (ffmpeg) at 320 Kb/s.

For me are transparent all, but using spek, I know than frequency analysis is only a part of quality mesurement, I see some differences:
- opus cut frequencies greater than 20 KHz, qaac greater than 17 KHz and ffmpeg 16 KHz.
- maybe is not important but the opus seems more "clean" than qaac

Interesting, thanks! Which preset did you use with qaac?
Can you also try out qaac (apple acc) with its default --tvbr 91 preset? Thanks

[tebasuna51]

Originally Posted by chros

Can you also try out qaac (apple acc)

Yes this is the qaac I used, and TVBR presets are:

-V 91 Overall bitrate: 496.532kbps (cut at 18.5 KHz)
...
-V 64 Overall bitrate: 340.74kbps
-V 54 Overall bitrate: 302.205kbps

With CVBR presets:

-v 320 Overall bitrate: 342.338kbps (cut at 17 KHz)
-v 288 Overall bitrate: 307.468kbps (in the image with cut at 16.5)

Talking about cut frequency the Opus 320 Kb/s is like AC3 640 Kb/s

[chros]

Originally Posted by tebasuna51

Yes this is the qaac I used

Oh, thanks!