Jump to content

Understanding the "Settings/Audio/Audio Info" Chain (ReplayGain, dither, etc.)


Recommended Posts

Hi. I'm hoping someone can help me understand some aspects of the process depicted in the Audio Info section.

I can't seem to take screenshots on my DAP, so I'll just describe the relevant features of what I'm seeing:

I'm starting with a 16 bit FLAC file. Under the DSP, I see a conversion to a Float64/32 bit. Then, under "Output", I have a "Direct HD" 24 bit since that's what I've manually set under the Output settings.

My primary question is: at what stage of this process is ReplayGain applied? I'm thinking of this question in regards to any distortions it could have on the audio. For example, I know that if you take a 16-bit file and digitally de-amplify it, you risk pushing those samples with amplitudes at the bottom-most steps down to the noise floor because you'll run out of bits. I read somewhere that if you take a full-range (peaking at 0 dB) 16-bit file, digitally de-amplify it by -18 dB, and save it as 16-bit, you're effectively encoding a 13-bit file.

As far as I understand it, this is essentially what ReplayGain is doing (digital de-amplification), so, if the gain is applied directly to the 16-bit file, one would probably see some information loss. (Whether one could hear it is a different story.) I'm not sure how the floating-point nature of the converted file (under "DSP") affects things, but, with the much larger bit depth afforded by the 32 bit structure, I can't imagine running into any information loss if applied at that stage in the process.

For the "Output" stage, I originally did not have the "Hi-Res Output" option enabled and so it was outputting a 16-bit file. My thinking went: even if there was no information loss at the DSP step, if it's then down-converting back to 16-bit, it won't actually avoid the issue because it's just restricting the bit-depth again at the end. The 24-bit structure has such a larger bit-depth that, according to my napkin math, you would need an extreme value for your ReplayGain tag to yield any information loss when applied to a 16-bit source file.

So, I'm supposing that, if the ReplayGain is applied at the DSP stage, then there shouldn't be any information loss with this setup.

On a related note, is there dither applied between the "DSP" and the "Output" stages (32-bit -> 24-bit)? I don't see any mention of it and it seems like a lot of processing for the machine to be doing on the fly, but it would seem to me an odd omission especially when it was originally outputting a 16-bit file to the DAC.

Please let me know if I've misunderstood something here. I'm relatively new to these audio engineering concepts. Thanks.

ReplayGain is applied as part of the DSP process (so within the internal 64/32 float stage). The point of it is usually to reduce the gain rather than increase it, but in the case of a very low level recording it could go the other way. 

Andre

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...