Recommended LC-AAC 5.1 quality setting?

[Winston_Smith_101]

I would like to transcode lossless 5.1 DTS-HD and Dolby TrueHD Audio into lossy 5.1 LC-AAC (Nero AAC Codec) to save space. What -q quality setting would still sound transparent at your experience?

Wikipedia: (https://en.wikipedia.org/wiki/Advanced_Audio_Coding)
Tests of MPEG-4 audio have shown that AAC meets the requirements referred to as "transparent" for the ITU at 128 kbit/s for stereo, and 320 kbit/s for 5.1 audio.

Does that mean you would recommend -q 0.3?

[SeeMoreDigital]

Is there any particular reason why you don't want to use HE-AAC?

[Winston_Smith_101]

Is there any particular reason why you don't want to use HE-AAC?

Yes, there is a reason. HE-AAC uses "Spectral band replication" (SBR). Since SBR generates high frequencies only synthetically, no transparency can be achieved with HE-AAC in contrast to LC-AAC.

[lvqcl]

As far as I remember, neroaacenc -q 0.3 creates HE-AAC files (avg. bitrate is ~84 kbps for stereo files).

[kuchikirukia]

QAAC q63 or higher. If you're not looking to skimp, q91 and q109 are popular settings.

[Winston_Smith_101]

@lvqcl: You are absolutely right. I meant q 0.4. I was so tired last evening, I have not remembered the exact number. 0.3 is to low. :)

@kuchikirukia: Thank you! I did not know QAAC at all. After what I could read the Apple AAC codec is really better than Nero AAC. I am not looking to skimp, i am looking for high quality transparent sound without wasting space. I will try that q91 and above settings.

You guys helped me a lot!

:thanks:

[tebasuna51]

Use q91 TVBR (-V 91) with QAAC is, more or less, equivalent to use -q 0.5 with NeroAacEnc.

QAAC is better than NeroAacEnc at low bitrates, at high quality like this can't be tested, both are transparent.

In my test I obtain 450 Kb/s (-V 91 qaac) and 443 Kb/s (-q 0.5 Nero) with the same 5.1 sample.

If you want 320 Kb/s you can try the CVBR mode with QAAC -v 320 (v lowcase)

With the same sample I obtain:
Nero 5.1-48 | Qaac 5.1-48
------ -------- | ------ --------
q 0.35 266 Kb/s | -V 54 277 Kb/s
| -V 64 314 Kb/s
q 0.4 325 Kb/s | -V 73 351 Kb/s
| -V 82 385 Kb/s
q 0.5 443 Kb/s | -V 91 450 Kb/s
| -V 99 507 Kb/s
q 0.6 545 Kb/s | -V 109 581 Kb/s
| -V 118 638 Kb/s
q 0.7 738 Kb/s | -V 125 704 Kb/s
q 0.8 796 Kb/s |
q 0.9 914 Kb/s |

Of course quality mode can obtain different bitrates with different samples.