Notes by ff123
Listening test conditions: Beyerdynamic DT 990 Pro headphones, fanless computer operation, mp3-to-wav conversion performed with the MAD 0.12.3 beta 4 plugin for Winamp. Encoder: Fraunhofer FastEnc and VBR implementation found in Cool Edit Pro with the MP3 ME plugin.
I decided to perform a VBR/CBR listening test using velvet.wav (found on the Lame test samples page). I had previously noticed in a quick listening test that Fraunhofer's VBR files were producing unexpected artifacts using this clip at 70% and 100% VBR quality.
If you compare this listening test against my previous listening test using velvet.wav (which was done with the same headphones and at the same volume), you'll see that I seem to have improved my listening sensitivity at 128 and 160kbs.
Using VBR, I can hear an additional type of artifact besides the swirling sound (like the sound of someone sharpening knives). It is an echo sound which beats in time with the cymbals, except it occurs in the opposite channel. This artifact remains even at 100% VBR quality, while at 192 CBR, there are no background artifacts that I can detect, and I have to concentrate instead on the smear of the scraping instrument in the right channel.
| Rank | Setting | Bitrate | ABX Results | Comments |
| 1 | 256kbs CBR | 256 | 12 of 16 | still concentrating on relative smear of scraping instrument |
| 2 | 192kbs CBR | 192 | 14 of 16 | concentrating on smear of scraping instrument |
| 3 | 100% VBR | 239 | 15 of 16 | echo sound in right channel with same beat as cymbals |
| 4 | 160kbs CBR | 160 | 16 of 16 | swirling noises in background |
| 5a | 70% VBR | 179 | didn't bother | swirling and echo sounds; on a par with 128kbs CBR |
| 5b | 128kbs CBR | 128 | didn't bother | swirling sounds; on a par with 70% VBR |
| 6 | 50% VBR | 149 | didn't bother | swirling and echo sounds |
Conclusion:
VBR isn't always automatically better than CBR, at least using Fraunhofer's implementation. In this case, 192kbs CBR easily beats 100% VBR.