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Topic: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included] (Read 5514 times) previous topic - next topic
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Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

CASE 1

Got a CONSTANT bitrate AC3 file here claiming192 Kbps on MediaInfo

However on spectrals:



I get this.

Frequency cutoff on zoom is clearly 20.5 kHz. So is this AC3 320?  If so why is MediaInfo reporting 192 :/

CASE 2

Also I have this VARIABLE bitrate AAC file....someone is claiming is 192 Kbps on average - how do I even check this?
 
I checked it's spectral here:



Frequency cut-off at about 18.5 kHz....so.....what bitrate is this?

So lost here on what's what with these files bitrate wise!

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #1 –
1) Wider spectrum is not equal to better sound quality. High frequencies are vulnerable to masking effect, it is not alwais necessary to spend bit rate to precerve them. High-quality encoders are designed with this fact in mind.
2) Higher bitrate is not equal to wider spectrum
3) Higher bitrate is not equal to better sound quality. The sound quality depends not from the "beauty" of the spectrogram and not from the bitrate. The sound quality largely depends on the artifacts of compression (which are not visible on the spectrogram). А high quality encoder may give you better sound on lower bitrate (even despite the narrower frequency range!) than а low-quality encoder.
4) AAC is not equal to AC3 from the point of coding quality. In fact, AAC usually is better soundwise at same bitrate than AC3.
5) Given all the above, the answer to your question "Are these AC3/AAC files REALLY 192 Kbps?" is "yes, it's more than possible" :)

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #3 –
What about it? It's their first post in nearly two years.

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #4 –
Has a 1000 batting average for paranoia. :D

I had a hunch;
and it was easier than finding a monthly lossy encode verification/xx.x kHz = xxx kbits thread.

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #5 –
Quote from: mpuzirew on
1) Wider spectrum is not equal to better sound quality. High frequencies are vulnerable to masking effect, it is not alwais necessary to spend bit rate to precerve them. High-quality encoders are designed with this fact in mind.
2) Higher bitrate is not equal to wider spectrum
3) Higher bitrate is not equal to better sound quality. The sound quality depends not from the "beauty" of the spectrogram and not from the bitrate. The sound quality largely depends on the artifacts of compression (which are not visible on the spectrogram). А high quality encoder may give you better sound on lower bitrate (even despite the narrower frequency range!) than а low-quality encoder.
4) AAC is not equal to AC3 from the point of coding quality. In fact, AAC usually is better soundwise at same bitrate than AC3.
5) Given all the above, the answer to your question "Are these AC3/AAC files REALLY 192 Kbps?" is "yes, it's more than possible" :)

Thank you. A lot to consider...but didn't answer my question sadly. How can I determine the exact Kbps number? I thought frequency cutoffs is EQUIVALENT to Kbps. I'm not talking about width of spectrum :/? I believe you mean spectrum height ?

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #6 –
Take size of file. Multiply by 8. Divide by length in seconds. There's your bitrate in bits per second.

Demux multi-stream files to raw bitstream files before performing this calculation, of course.

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #7 –
Quote from: ManifestDestiny on
I thought frequency cutoffs is EQUIVALENT to Kbps.
A funniest bullshit I ever heard :))
Kilobits per second (kbps) is amount of data spent to record a second of audio, this has no strict relation to  frequency (kHz) cuttoff :)

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #8 –
Quote from: mpuzirew on
Quote from: ManifestDestiny on
I thought frequency cutoffs is EQUIVALENT to Kbps.
A funniest bullshit I ever heard :))
Kilobits per second (kbps) is amount of data spent to record a second of audio, this has ABSOLUTELLY no relation to  frequency (kHz) cuttof :)

I'm just saying What.CD had this spectral analysis page  -

https://opentrackers.org/whatinterviewprep.com/prepare-for-the-interview/spectral-analysis/index.html

Where they claim frequency cutoff = certain Kbps ...is why I wondered

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #9 –
Quote from: ManifestDestiny on
Where they claim frequency cutoff = certain Kbps ...is why I wondered
There is no such a "=" claim! There are only examples that show that the cutoff frequency is lowered when reducing the bit rate. This is normal for lossy codecs. A lossy encoder generally try to save some bitrate for for the most distinguishable frequencies by NOT preserving some of high freq (which are less distinguishable).  This ensures the optimal bitrate/quality ratio. It should also be borne in mind that  all lossy coders are not the same. They are different, using different algorithms, having different sound quality at same bitrates. What is true for mp3, is not quite true for AAC etc. There's NO any STRICT relation beetween bitrate and cutoff.

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #10 –
Quote from: mpuzirew on
Quote from: ManifestDestiny on
Where they claim frequency cutoff = certain Kbps ...is why I wondered
There is no such a "=" claim! There are only examples that show that the cutoff frequency is lowered when reducing the bit rate. This is normal for lossy codecs. A lossy encoder generally try to save some bitrate for for the most distinguishable frequencies by NOT preserving some of high freq (which are less distinguishable).  This ensures the optimal bitrate/quality ratio. It should also be borne in mind that  all lossy coders are not the same. They are different, using different algorithms. What is true for mp3, is not quite true for AAC etc. There NO any STRICT relation beetween bitrate and cutoff.
Quote from: kode54 on

Not even for MP3s as described on the page?
Take size of file. Multiply by 8. Divide by length in seconds. There's your bitrate in bits per second.

Demux multi-stream files to raw bitstream files before performing this calculation, of course.

Does this apply to AC3 and AAC?

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #12 –
ManifestDestiny, I think, you were confused by the fact that AC3 had wider frequency range that AAC. But, this is absolutelly normal! AC3 is lower quality coder, it has more primitive psychoacoustic model than AAC. It's "not smart enough" to cut high-freqs in favor of quality. Instead, it "evenly spreads" the bitrate over the entire frequency range to the detriment of quality.

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #13 –
Quote from: greynol on
Can I ban this guy for TOS9?

9. All members must refrain from posting links to -- or information regarding how to obtain -- material that is copyrighted and being distributed without authorization or is otherwise illegal.  Discussion containing information of how to obtain such material, how to bypass protection methodologies of such material, or how to otherwise violate laws pertaining to such matters will not be tolerated.

That interview guide is very popular as a learning tool, regardless of the content of the site.  I'm linking to documentation, not anything else

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #14 –
Quote
Does this apply to AC3 and AAC?
If your question is about bitrate,  yes.  kbps is kilobits per second.    (And, there are 8 bits in a byte.)      It's a straightforward definition & calculation, except metadata (especially embedded album artwork) can throw-of the calculation because those non-audio bytes are taking-up file space. 

Re: Are these AC3/AAC files REALLY 192 Kbps? [Spectrals Included]

Reply #15 –
Quote from: greynol on
Can I ban this guy for TOS9?
No. There's no violation. Unless mentioning SoX and dbPoweramp already is enough to trigger ToS #9.

It's more problematic that the site itself is completely useless. You can only spot a transcode if you have the source and the transcoded file, and then you could just keep the original. Cut-offs in spectrograms can (deliberately!) happen during mastering, and are not necessarily a result of an conversion to a lossy format. And it might have even been converted to a lossy format by the producer before encoding for delivery. You can just never know. To obtain the best version available usually means to get the original audio CD.
It's only audiophile if it's inconvenient.