Originally Posted by Scott Wilkinson
I would not want to add to any clipping, so applying gain before SRC seems like not the best idea, at least in two out of the three tracks as you cite here. One question I have is, assuming that clipping is not an issue, does it make a difference if the gain is applied before or after the SRC? It seems to me that it wouldn't make a difference. If the gain is applied before the SRC, that would raise the noise floor, then the SRC would lower it. If the gain is applied after the SRC, the noise floor would first be lowered by the SRC and then raised by the gain. Either way, the result would be the same, wouldn't it? Or am I missing something?
Four options: (each processing step is between [ ] )
A [Gain +0.2(dither?) ] -> [-0.1 SRC16dither] -> [-0.1 SRC24 -0.1]
B [ -0.1 SRC16dither] -> [Gain +0.2] -> [-0.1 SRC24]
C [-0.1 SRC16dither] -> [0.1 SRC24] -> [Gain+0.2 (dither?)]
or D (4 steps)
[Gain +0.1] -> [-0.1 SRC16dither] -> [Gain +0.1 ] -> [-0.1 SRC24]
The SRC software applied the -0.1 gain change before the resampling and dither raises the 16bit noise floor slightly *after* the resampling.
Best practice is to apply processing in the 24 bit domain. This rules out option B
Touching the resulting 16 bit file and the 24 bit lo-res version with gain is not desirable. Purist may object to this.
The dither after the 24 to 16 conversion preserves some of the dynamic range of the 24bit file and applying gain may affect that.
Imo it's best to do the gain in the 24 bit domain on a copy off the hi-res file. It might raise the noise floor but, as it is hires, this noise floor should be lower than the resulting 16 bit file anyway.
Highly controversial but you could also consider to apply -0.2dB gain on the hires file first.
You can consider this as a mastering step to fit the purpose of the file.
Use that 'mastered' file in the comparison as the hires sample and create the lo-res version from it using any of the options listed above you like best.
This will negate the effect of the +0.2 gain could have on the clipped samples while preparing the lo-res version.
Best is to simply use SOX....