I've been researching this for a couple weeks now. I did a fair amount of ABX testing with various codecs at various settings. Here is one of the tracks I was able to ABX at ~96 kbps and ~128 kbps.
96 kbps Apple AAC TVBR:
foo_abx 1.3.4 report
foobar2000 v1.3.7
2017/01/12 18:30:07
File A: D:\Encoding\Gabriel, Peter\1986 - So\01 - Red Rain.m4a
File B: H:\Library\Albums\Gabriel, Peter\1986 - So\01 - Red Rain.flac
18:30:07 : Test started.
18:31:26 : 01/01 50.0%
18:32:55 : 02/02 25.0%
18:33:11 : 03/03 12.5%
18:33:31 : 04/04 6.3%
18:33:50 : 05/05 3.1%
18:34:02 : 06/06 1.6%
18:34:11 : 07/07 0.8%
18:34:20 : 08/08 0.4%
18:34:35 : 09/09 0.2%
18:34:58 : 10/10 0.1%
18:35:09 : Test finished.
----------
Total: 10/10 (0.1%)
128 kbps Apple AAC TVBR:
foo_abx 1.3.4 report
foobar2000 v1.3.7
2017/01/25 21:31:07
File A: D:\Encoding\Gabriel, Peter\1986 - So\01 - Red Rain.m4a
File B: H:\Library\Albums\Gabriel, Peter\1986 - So\01 - Red Rain.flac
21:31:07 : Test started.
21:31:27 : 01/01 50.0%
21:31:36 : 02/02 25.0%
21:31:47 : 03/03 12.5%
21:32:09 : 04/04 6.3%
21:32:31 : 05/05 3.1%
21:32:43 : 06/06 1.6%
21:33:09 : 07/07 0.8%
21:33:16 : 08/08 0.4%
21:33:34 : 09/09 0.2%
21:33:45 : 10/10 0.1%
21:33:47 : Test finished.
----------
Total: 10/10 (0.1%)
96 kbps Apple AAC CVBR:
foo_abx 1.3.4 report
foobar2000 v1.3.7
2017/01/25 20:59:34
File A: D:\Encoding\Gabriel, Peter\1986 - So\01 - Red Rain.m4a
File B: H:\Library\Albums\Gabriel, Peter\1986 - So\01 - Red Rain.flac
20:59:34 : Test started.
21:00:17 : 01/01 50.0%
21:00:42 : 02/02 25.0%
21:00:52 : 03/03 12.5%
21:01:00 : 04/04 6.3%
21:01:04 : 05/05 3.1%
21:01:11 : 06/06 1.6%
21:01:21 : 07/07 0.8%
21:01:28 : 08/08 0.4%
21:02:05 : 09/09 0.2%
21:02:18 : 10/10 0.1%
21:02:20 : Test finished.
----------
Total: 10/10 (0.1%)
128 kbps Apple AAC CVBR:
foo_abx 1.3.4 report
foobar2000 v1.3.7
2017/01/25 21:42:32
File A: D:\Encoding\Gabriel, Peter\1986 - So\01 - Red Rain.m4a
File B: H:\Library\Albums\Gabriel, Peter\1986 - So\01 - Red Rain.flac
21:42:32 : Test started.
21:42:59 : 01/01 50.0%
21:43:07 : 02/02 25.0%
21:43:12 : 03/03 12.5%
21:43:41 : 04/04 6.3%
21:44:07 : 05/05 3.1%
21:44:25 : 06/06 1.6%
21:44:40 : 07/07 0.8%
21:44:53 : 08/08 0.4%
21:45:09 : 09/09 0.2%
21:45:33 : 10/10 0.1%
21:45:34 : Test finished.
----------
Total: 10/10 (0.1%)
I failed both TVBR and CVBR at 160 kbps, but the lower bitrates were hardly what I could call terribly annoying. There were some tracks where I failed even at 96 kbps. I haven't noticed any discernible difference between TVBR and CVBR in my ABX testing yet, so I'm wondering what would be the reason to use one over the other.
Do you have any examples of tracks where you were able to ABX the TVBR at a given bitrate but not the CVBR at the same bitrate?