[opus] 133 kbps stereo killer sample

[Agustín Dall'Alba]

I halved the volume of the sample before encoding with
`sox -v 0.5 floex.wav quiet.wav` and now I can't ABX it succesfully anymore.
So the artifact I heard was just clipping when encoding or decoding.

Opus remains unbeaten for me at 133 kbps. That's totally awesome.

Cheers

On 10 April 2017 at 17:14, Agustín Dall'Alba <agustin at dallalba.com.ar> wrote:
> Hello! I found a sample I can ABX successfully when encoded at
> 133.333 kbps. I was targetting 1 MB/min.
>
> https://drive.google.com/drive/folders/0B8KWShoIrA1kQzR1Z0FFRUlfcEU
>
> floex.wav is 4:54–5:04 of a lossless copy of 'Forget-me-not' by
> Floex, downloaded from http://store.floex.cz/album/zorya
>
> floex-133.opus was created with `opusenc --bitrate 133.333333 floex.wav
> floex-133.opus`, opus-tools 0.1.9 (using libopus 1.1.4).
>
> I used a Sony MDR-V6 pair of headphones and my laptop's oonboard audio. I
> detected the artifact when I was listening casually from my phone with the
> same headphones.
>
> In the second to last note of the crescendo (at ~5 s in the sample) there's
> a slight flutter in the original that turns more prominent and tape-like
> after encoding.
>
> I also tried encoding at 128 kbps and 150 kbps.
>
> ABX results:
> - floex-133.opus.wav 10/10, p-value<0.001
> - floex-150.opus.wav 4/10, p-value<0.83
> - floex-128.opus.wav 17/20, p-value<0.002
>
> Only at 150 kbps is Opus transparent to me for this sample.
>
> Cheers