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Topic: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8) (Read 967 times) previous topic - next topic
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Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Hello. I detected that 22050Hz 48kbps mono cutoffless LC-AAC encoded by FDKAAC has almost no holes in the spectrogram while 22050Hz 56-or-64-kbps (I didn't try beyond that) mono cutoffless LC-AAC encoded by FDKAAC contains some holes in the spectrogram. I know that a fuller spectrogram does not mean better quality (as TOS#8 says) and I don't say the 48kbps one has a better quality, but seeing that a higher bitrate results in a more holey spectrogram on a fully MDCT-based codec (AAC-LC) surprised me because of the working principles of those codecs. Does anyone know why and which one has higher quality?

(I attached the files below, and they are very short because they are fair use. I could use a freely licensed sample but I made my comparisons with this music and I wanted to use the same music to keep things easy. Fair use credit: Sonic Heroes by Crush 40 (per metadata).)

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #1 –
 ;) 
I was going to post something similar to this, but now I think don't need to. This is already near (and it's about FDK-AAC too)
It's more tricky because it involves ELD profile and SBR, but I can get 500kbps files sound quite bad, with a lot of spectrum holes. Up to 1 Mbps when using downsampled-SBR or no SBR at all (though then it lacks support of sample rate higher than 48KHz). (The bitrates mentioned were for 44.1 KHz stereo, other layouts and settings can result in different bitrate ranges :P)

In this case quality is obviously worse than usual. At less bitrate I have good quality files, but for some reason at these higher rates the encoding gets... "outstanding"  :D.
It is so bad, that .zip can seriously compress the resulting files.

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #2 –
Quote from: a.ok.in on
;) 
I was going to post something similar to this, but now I think don't need to. This is already near (and it's about FDK-AAC too)
It's more tricky because it involves ELD profile and SBR, but I can get 500kbps files sound quite bad, with a lot of spectrum holes. Up to 1 Mbps when using downsampled-SBR or no SBR at all (though then it lacks support of sample rate higher than 48KHz).
In this case quality is obviously worse than usual. At less bitrate I have good quality files, but for some reason at these higher rates the encoding gets... "outstanding"  :D.
It is so bad, that .zip can seriously compress the resulting files.

Sorry, I couldn't understand, which file is better in your opinion and why?

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #3 –
Quote from: Klymins on
Sorry, I couldn't understand, which file is better in your opinion and why?

The smallest one. As it has quite similar quality it should be preferred over the other file.

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #4 –
Quote from: a.ok.in on
Quote from: Klymins on
Sorry, I couldn't understand, which file is better in your opinion and why?

The smallest one. As it has quite similar quality it should be preferred over the other file.

Thanks, but I noticed that I actually feel like the 56kbps one has a higher quality while it gives a more holey spectrogram. It's almost like the 48kbps uses SBR (but it should not because it's AAC-LC). Does anyone know what's happening?
 

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #5 –
Codec probably used extra bits for frequencies that matter for that sample, leaving less bits for those which don't matter, and in the smaller file it just couldn't justify that considering the bitrate. It's stuff that's around 60 dB below the program, so it could be considered noise anyways.
TAPE LOADING ERROR

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #6 –
Quote from: itisljar on
Codec probably used extra bits for frequencies that matter for that sample, leaving less bits for those which don't matter, and in the smaller file it just couldn't justify that considering the bitrate. It's stuff that's around 60 dB below the program, so it could be considered noise anyways.

But the spectrogram shows SBR-like patterns and I hear some softening (SBR-like, unwanted) on the 48kbps file, do you know what causes this?

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #7 –
Low bit rate encoding will almost always include audible artifacts. Different encoders will handle the audio differently, they don't all have same psycho-acoustical models.
TAPE LOADING ERROR

Re: Higher bitrate gives a more holey spectrogram in FDKAAC (with respect to TOS#8)

Reply #8 –
Quote from: itisljar on
Low bit rate encoding will almost always include audible artifacts. Different encoders will handle the audio differently, they don't all have same psycho-acoustical models.

I know, but these artifacts does not sound like the classic MDCT artifacts that occur at different bitrate-samplerate combinations (for example 10kbps 11025Hz mono).