derp1n
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Can you prove this?if a piece of audio is converted from WAV (CD) to MP3 to FLAC, the audio levels don't get changed
Can you prove this?if a piece of audio is converted from WAV (CD) to MP3 to FLAC, the audio levels don't get changed
Interesting! So you think there is a difference? I was similarly challenged by someone on head-fi some time ago. He was an audio expert or liked to think of himself as one, and a great admirer of Apple's iPhone. Other than the equivalent quality, he kept mentioning gain of space as a side benefit of 320 kbps (to which I replied storage space wasn't an issue to an Android user). So I got challenged to take some kind of scientific (pseudo-sientific?) procedure of his own chosing to satisfy his claim. Instead I offered to rip a 320 kbps track and compare it to the same track in FLAC and try an honest comparison. It was a song by Brazil's Caetano Veloso, a world-class performer always surrounded by top musicians. I chose to focus on the very sophisticated percussions part in that song. The loss of detail was very obvious. In brief, the FLAC version made it possible to hear the percussionist play actual melodies ; on the 320 kbps version there were just thuds with no sense of melody. I reported my "findings", suggesting he perform the same test, but he never bothered to even reply. Not scientific enough I guess. I remember him mentioning level matching, I have no idea if my levels were matched, but I doubt it would have made a difference in this case: when a detail is not there, it is not there.
That claim seems to surface quite often, it appeared recently on a YouTube channel I'm a subscriber to ; the author was justifying the fact his new recording would only be available in 320kbps and the purpose of the episode was to prove there was no difference (if you thought differently you were an "audiophool").
Yes easily. Just take a piece of audio, find the peaks and make a note of the peak levels. Convert to MP3 and check the peaks again. They'll be the same. As far as I know, there's nothing in the MP3 encoding algorithm that affects peak levels. There's also nothing, again as far as I know, that affects overall energy and hence perceived loudness.Can you prove this?
Yes easily. Just take a piece of audio, find the peaks and make a note of the peak levels. Convert to MP3 and check the peaks again. They'll be the same.
Well, the levels were the same from the device (smartphone) I was using, at least. I wasn't using any special computer programme. I guess I don't understand how a detail is supposed to appear with a different volume if it is no longer there.I haven't used every piece of conversion software out there, so this may be universally true, but I don't know. Nonetheless, given the criticality and repeatedly demonstrated audibility of small level changes, I'd still spend a minute or two verifying it before beginning a test.
Phase shifts are audible with headphones. It is in rooms with reflections where audibility becomes very difficult. Here is Dr. Toole from his book
Level matching is absolutely necessary since our ears are extremely sensitive to small level changes, while not necessarily perceiving the difference as being level. No level matching, the test is invalid.
Definitely. Just not easy to find on all tracks and for all people. Here is my sample results:Interesting! So you think there is a difference?
A quick example:Actually, for MP3 vs PCM conparisons, the best reference for level matching is the MP3 encoder itself.
If you try to match levels using, for example, the RMS level of both samples, there is a risk that, if the original had a lot of energy above 16 kHz, your measurement finds the mp3 to have an inferior overall RMS level, because these frequencies are missing.
However, matching the RMS level this way, all you are going to do is actually mismatch the level of the remaining audible frequencies, to compensate for the disparition of the inaudible content above 16 kHz !
Comparing the peak level of the PCM and the MP3 samples is worse : because of the change in frequency content, all square and step waveforms are changed. The overall level is unchanged, but the peak level can vary a lot. +1 dB on the highest peak for the mp3 file is common.
To compare a PCM file with an MP3, use a command line encoder, or at least a software that you perfectly know, so that you can make sure that the MP3 is not normalized (that would be surprising), that if it features Replaygain information, then you don't use it during playback to adjust the volume, and that in the mp3 file, the highest peak level detected by Replaygain is not above 0 dBFS (that is "1" in the replaygain informations).
This links talks about mp3gain, a software used to change the volume of mp3 files. You can also change the volume of your original WAV files the same way, with Audacity, for example.
If you don't change the volume, neither of the original, nor of the MP3, they are matched by default. That's what I mean with "a software that you perfectly know"... So as to make sure that there is no mp3gain option or something enabled by default somewhere in a hidden menu.
A perfectly defined set of rules minus one point, to be definitive they results should also be repeatable.
If a A-B test resulted in 95% correct answers, it is obvious that result should be repeatable.
If it was not repeatable we could probably assume the presenter was not honest in his presentation in some way.
No your in the majority, have a look at the frailty of eye witnesses.. yet the law says..I'm probably in the minority. For me, the evidence I need is obtained from extended listening to the device in the same way that I would normally enjoy such a device. And as for sounding good, I do have some pretty stringent nit picky ideals, which not everybody shares. So I think suffice it to say it has to sound good to me.
I would use people whose listening descriptions tend to match mine to see if some gear would be interesting to check out as well. However, I usually also would like it to meet some somewhat low standards for measurements. For instance, say an SNR of above 75, THD of less than 1%, <5% for tubes. A wide bandwith 20-20khz with no huge amounts of roll off. Though this doesn't preclude me from tube amps, I would prefer an amp to handle a 4 ohm impedance as well. If it's a DAC, at this stage I would prefer it to process 96khz files as I have several of them from my recordings. In the future, it would be nice if they could do 192 khz files. Luckily most DACs nowadays do 192 khz without issue.