I do personally believe external component reviews are the hardest reviews to accurately write. Impressions and expectations can vary extremely widely from reviewer to reviewer. Hence, I’ve added a section describing my testing methodology for overall sonic thoughts to help you understand how to interpret and relate my impressions in a way that will be useful for you. This is actually extremely important information, but spoiler tagged as it is quite long.
The majority of the sound signature alterations and sonic attributes you will experience is primarily due to #1) your source files #2) your headphones. Hence, it is extremely important to control these two variables when testing a dac/amplifier. Excluding the source files, headphones will have the greatest contributions to any improvements in sound quality you hear and I do believe that a dac/amplifier combination will never contribute to more than ~20% of the overall sound quality. Realistically, the number is usually closer to 5-10% in my real life experiences. This is just my personal opinion from my personal experience. Feel free to have a different opinion, but this will give you a relative sense of the scale that I am referring to.
Source Files: I primarily use Spotify Premium (320kbps Ogg Vorbis) during my testing as I personally have tested myself to rarely be able to distinguish the different between lossless and lossy during double blind testing. I can distinguish between higher and lower bitrates of lossy files, hence only 320kbps files are used. However, I do also use Tidal Hi-fi and FLAC files just to be complete. I will not delve into writing about differences heard using the Astrapi between lossless and lossy as I know that I am not a reviewer that can reliably and consistently distinguish between those formats under blinded conditions.
Headphones: Some sonic characteristics may be more overly emphasized/underemphasized with specific headphone pairings. Other sonic characteristics may inherent to the headphones being used. Therefore, I test primarily using the same pair of headphones (the Oppo PM-3). Then if there are sonic aspects that I believe to be inherent/attributable to the Oppo PM-3, I will test further by using a different pair of headphones that do not have that sonic attribute.
What do the terms I use mean: None of the ‘flowery’ audiophile words I use mean anything other than the way they are defined here:
http://www.head-fi.org/a/describing-sound-a-glossary. These are specific terms that I am applying as I am listening to particular regions of the frequency response. Not poetry.
How to interpret what I mean: How do I know which word to use? Well, I do extensive direct A/B testing using the same track (limited to <30 seconds with <5 second swap time) on the Astrapi against a control (either with no external components or with a different dac/amp combo). I use Audio Switcher, a hotkey program to rapidly switch between set-ups (found here
http://sourceforge.net/projects/audioswitcher/). Each time I do a direct comparison, I will only focus on one particular region of the frequency response and listen for relative differences between my control and the Astrapi. It is an extremely tedious process, but the only accurate way to really determine sonic impressions in a way that can be useful to readers that may have vastly different background experiences, expectations, and goals (imo).
So the terms I use are RELATIVE terms on differences between the Astrapi against the control or my personal preferred sound. NOT absolute terms. Any statement on what things should sound like will be analogous to how things sound like through my primary preferred set-up (Schiit Bifrost Uber > Schiit Lyr 2 > HE-560). Therefore, if your primary set-up or preferred sound is different, your experience will be different!! You will need to find a common shared reference point for my impressions to be useful.
