- Aug 18, 2017
What is tough is that the difference is so high. That is, if original file and recording is -44 dB PK Metric, we can confidently say that the reproduction chain is not transparent to the digital file but the question is what is the difference? To use a statistical analysis, you can run an ANOVA but the Tukey Post Tests help you hone down on more details.
I’d get that sort of score with a UB9000 to Topping PA5 to E1DA Cosmos which should be reasonable, except for my recording level being lower where noise may in fact dominate.
Is that noise noticeable only if I were to raise the recording to a theoretical +0 dB?
That is, the source recording has no reference volume. Presumably for a digital file with reasonable dynamic range in a 24 bit container, you could have 120 dB true dynamic range out of 144 dB and let’s say it’s movie standard so 124 dB average, 144 dB peaks, and noise of 24 dBz. When compared to a recording that may reflect 70 dB average volume, 90 dB peaks, the noise in the system is going to dominate, and when the PK Metric level matches to the recording level to the digital source, the noise will really rise!
I guess question #2. For level matching, does DeltaWave match comparison volume to the reference volume? At which point I should have the recording as reference and digital source as comparison? Or does DeltaWave raise the volume of the quieter file to the louder one?
It’s an easy test but I am admittedly away from my desktop right now…
This is why DeltaWave includes various other analysis tools. PK Metric is just the perceptually-weighted version of the difference file. There are about 20+ other analysis tools built into DeltaWave to let you study the differences between two files in minute detail.
DeltaWave corrects for all the major linear errors between reference file and comparison. It does it by applying corrections to the comparison file, never to the reference. The default linear corrections include:
1. Phase error correction (delay removal) up to a tiny fraction of a sample
2. Level matching, including DC offset removal
3. Clock drift removal when two devices are used that run off different clocks (like in your example)
4. Option to trim front and end of the recording if the equipment doesn't start recording at 100% (can be caused by digital filters, PLLs that don't sync right away, fade-in volume controls, etc).
For other types of errors, like those caused in the frequency (and phase) domain by filters, for example, DeltaWave also provides tools to account for those, but these are more advanced tools and require some understanding of what you're doing. The basis for these tools is blind deconvolution.
Once linear differences are removed, DeltaWave computes various metrics, including RMS null and PK Metric (also DF Metric, and others). Which one you use is up to you, but you need to understand the purpose and the limitations of each.