Hi Maks Karpov, I observed similar quality degradation on some of my voice samples, and sent pathological samples to David for analysis. What I can say for sure is language has nothing to do at all. I fixed my problems by lowering audio input levels, filtering of input to take out very low frequency and very high frequency components and adding some comfort noise to smooth out clipping artefacts.
Adrian On January 11, 2020 12:08:56 PM UTC, "Макс Карпов" <initrd....@yandex.ru> wrote: >Sorry for sending HTML message, I didn't expect it to mess up the >archive. > >Plaintext copy of previous message follows: > >------ > >Hello! > >Recently I had tested Codec2 on audio samples on both English and >Russian languages, using MELPe as a reference. Moreover, I used three >noise modes: no noise at all, gaussian noise and voice noise (e.g. when >you are talking in a crowded room). As I don't have a source code for >MELPe 600, I had tested only 1200 and 2400 bitrates. Some of MELPe >tests were repeated in a environment where encoder and decoder >processes were separated to ensure that no audio information is leaked >through internal buffers and structures. > >To my disappointment, however, Codec2 performed much worse than MELPe, >producing yet still intelligible (in some cases), but heavily distorted >result. I made page with original and encoded samples: >https://m-k.mx/static/codec2/. > >I am surprised why Codec2 performs so bad even on high bitrates where >MELPe produces almost identical audio without any audible artifacts. >Codec2 also degrades significantly on non-English samples (VQ codebooks >are fine-tuned for English?). While degradation at noisy samples is >expected (especially in voice noise), Codec2 sometimes produces very >distorted and hardly intelligible results, while MELPe exhibit only >slight degradation. > >So my questions are: > >1. Are my experiments correct? Maybe I'm missing something important, >like equalizer in front of Codec2 (--eq option appears to have no >impact on the quality). >2. Are high-bitrate modes like 2400 and 3200 still up-to-date? I have >seen a lot of effort put into 700C mode, but sometimes high-bitrate >modes are useful as well. > > >_______________________________________________ >Freetel-codec2 mailing list >Freetel-codec2@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/freetel-codec2
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