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Topic: Can headroom worsen audio quality due to the masking threshold? (Read 1786 times) previous topic - next topic
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Can headroom worsen audio quality due to the masking threshold?

I know this may sound like a silly question, but while I know it is a good idea to add headroom before encoding with a lossy codec such as MP3 or AAC to avoid clipping, can this, due to how these codecs work, result in more audio being classified as unimportant and being mangled compared to encoding a 0 dB peaking file because more of the audio goes under the masking threshold?

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #1 –
Same could be said about lossless, that by adding headroom you decrease number of bits used / signal-to-noise ratio.
Lossy codecs are supposed to be transparent even for very quiet passages, quality you lose that way is so microscopic that probably unmeasurable/undetectable.

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #2 –
Masking is relative...  If A is 20dB louder than B and they are close in frequency, B is likely to be masked.   That 20dB ratio doesn't change when you adjust the volume up or down.   Of course, if the volume is low-enough, B may be so quiet that it's not audible by itself without the masking.

Plus, 1dB or so of change is pretty insignificant.

I've never heard the clipping caused by an MP3 going over 0dB so personally I don't worry about it.   I've got tons of MP3s ripped from CDs that "show clipping" in Audacity.     And I've never heard of anyone else hearing it either.  I've never heard of a related controlled listening test (which would have to be level-matched).

If you hear a compression artifact it's probably something else that won't go-away at a slightly lower level.

BTW - The MP3 isn't actually clipped.  It can go over 0dB without clipping.  But you'll clip your DAC if you play it at "full digital volume".

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #3 –
Quote from: fred-hy on
I know this may sound like a silly question, but while I know it is a good idea to add headroom before encoding with a lossy codec such as MP3 or AAC to avoid clipping, can this, due to how these codecs work, result in more audio being classified as unimportant and being mangled compared to encoding a 0 dB peaking file because more of the audio goes under the masking threshold?

Try testing with your favorite encoder in VBR mode and see how much you have to lower volume before the bitrate starts decreasing significantly. 
 

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #4 –
I remember from a somewhat long time ago (back when I didn't know which MP3 encoder does Flash use) that GXLame (in CBR mode) puts significantly more empty spectral areas with a lower volume (non-extremely, I'd say the difference is lower than 10dB). But this was a very sketchy comparison. And TOS 8 applies.

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #5 –
some codecs are better than others at compensating for this.
iirc, Opus doesn't use a fixed noise floor.
Musepack encoder can be manually tuned (--ltq_gain) so you can put negated ReplayGain value there for example.
but actually *hearing* the difference caused by this will be impossible on most material of course.
a fan of AutoEq + Meier Crossfeed

Re: Can headroom worsen audio quality due to the masking threshold?

Reply #6 –
Apple's AAC encoder is known to use less bitrate for quiet signal.
As for MP3 or AAC-LC, you can encode at loud level and then you can change the volume by mp3gain or aacgain.