Those last tests I ran inspired me to do another music-based test. This is the same 16/44.1 music file: 58 second sample from Opeth's "Ghost of Perdition," WAV ripped from a CD I own. It starts right after that few-second intro and continues through that heavy, satan-music passage. Sure, it's not a reference-quality track, but it represents what I regularly listen to...it's actually the one track I primarily use to judge equipment (more for overall tone and performance than pure technicalities), just because I'm extremely familiar with it. In other words, if I get something that sounds perfect on this track, it's almost guaranteed I'll like it for everything else. I'm open to tests specific tracks or other things if you suggest them.
What I wanted to do for this test was zoom in on a relatively small range of frequencies to get a better view of the subtle changes brought from software upsampling. And, given that a NOS DAC has more and more "difficulties" with higher frequencies, I figured I'd focus in that area. I chose to look at the 10.5-11KHz region, which is an area a NOS DAC will struggle with but still contains useful musical information. I adjusted the dB range once I figured out where the average result would sit.
This test is also done "by hand," so it's not perfectly accurate or precise all the time. I start the playback in JRMC and then record in ARTA as quickly as I can. I manually stop recording shortly after the sample hits the 58 second mark. The ADC can also produce odd results at times when fed a signal with a sample rate that is or a multiple of 44.1KHz, so there's the potential these results have garbage in them. I'll eventually pick up a device that has more options and wider compatibility in this regard, but it does OK for now.
This test is also done as an exp. average over the sample and not a snapshot of any one moment. A potentially better way to look at the results would be to see the output over time (not spectrum), but given I start/stop everything by hand, it's very difficult to get that matched up. (I'm sure there are ways I could set this up for high precision and accuracy, but I'd have to look into that and am frankly not concerned enough to.)
To help make up for these "by hand" tests, I did 3 runs through JRMC without any software upsampling, and then I did 3 runs with 176.4KHz upsampling. (First three pics are without, last 3 are with.)
What is particularly interesting is how consistent the upsampled results look compared to the non-upsampled. And while there are some clear differences between w/without other than overall amplitude, they do still hold many similarities (at least, if you compare the w/without results that look the most similar...obvious, haha). Inaccuracies aside, I was looking to see if the results would be in any way different and still repeatable, and that was indeed the case to some extent.
Eventually I will measure this on something objectively better so that these tests can be compared against a known reference.
