- Introduction: http://www.head-fi.org/t/800208/#post_12386876
- Tutorial/Guide: http://www.head-fi.org/t/800208/#post_12386879
- Overview of all Measurements: http://www.head-fi.org/t/800208/#post_12386883
All right folks, I have been planning to start this thread/topic long ago here on Head-Fi as I was an active guy on that topic in a German online audio community I was a very active and leading member in the past years, but was just too lazy and lacked the required time to write the introduction, tutorial and so on here. What I am talking about are (quite simple) audio/source device measurements that everybody can do with his/her (Windows) computer (given that the input that is used for recording has got a as flat as possible input response).
The first post should be seen as an introduction to the topic, the second is a tutorial of how to easily measure source devices (and how to see whether one's audio interface is suitable or not) and the third an overview of measurements in this thread and on other websites.
For a DAP/DAC/Amp, the most important things for me are a strictly flat unloaded frequency response (not that difficult to achieve, but very few devices still fail to reproduce it), as low as possible noise floor (hiss), low output impedance (lower than 1 Ohm is a must for me, as I am using mainly multi-driver in-ears with varying impedance response over their frequency spectrum) and no roll-off in the bass with a low impedance load (the lack of caps in the signal path is required for that and fortunately most recent devices don't fail this test) plus load stability (difficult to measure with my rig, but more about that in a second). That's an objectively (sonically) perfect audio device for me and I actually don't care too much about its price point, marketing or even my subjective perception of its sound quality, as when properly volume-matched (but not fully blind-folded), if numerous devices are about comparable in terms of the just-mentioned things, the difference in "sound quality" is extremely minute, close to inexistent in most cases (and to hear them, really hard concentration is required). And the still remaining differences can mostly be explained by things like noise floor, noisefloor shaping, THD (sometimes) and stereo crosstalk (given that the output impedance is low, of course). And still, the differences are extremely subjective under that conditions without a real blind-folded test. I'm not saying that it isn't legitimate to still speak about subjectively perceived audio quality (and I even still do it either, but it is important to note that it is my personal, highly subjective perception), even if they can be placebos based on the mood, new toy syndrome, build quality, marketing, attitude towards the product/maker, expectations or whatever (which however doesn't matter for our brain which will still translate those to perceived superiority).
That's why when I buy/review/get my hands on an audio device like DAPs, Amps and DACs, the first thing after initial listening for a few minutes (very rarely, I even skip that part) I do is to put a Micro SD card with the RMAA test file into the device and play it back (unloaded) while it is being recorded with my soundcard, which takes just barely more than one minute. Then it can be analysed in the RMAA application (freeware for Windows). Afterwards, I perform a loaded measurement for which I am using the Ultimate Ears Triple.Fi 10, as it has been a common model for performing RMAA measurements in that German audio community (with that, there was also a good consistency between various enthusiasts of us who posted their measurements). A different multi-driver in-ear with varying impedance response that reacts critically in combination with a device that has got a high output impedance will be sufficient as well, of course.
Having done that, I then know whether the unloaded FR is flat, I can calculate the output impedance based on the IEM's impedance response and the FR output deviation with the just measured source device or just see whether the deviation is really small (which means that the OI is very low; I also know how the FR deviation of the T.F10 looks with certain OI values like 0.1, 0.5 and 1 Ohm) and I can see whether there is a roll-off caused by caps in the signal path.
The hiss test then just requires listening and the load stability is nothing I can really accurately measure, as my audio interface (actually just my laptop's audio input which is however perfectly flat even down to below 20 Hz, where many interfaces unfortunately show a roll-off) is somewhat too simple to even get comparative results of SNR, Crosstalk etc. within my own measurements (and most importantly, besides FR and FR deviation, measurements between different devices that are taken to record the signal shouldn't be made, as they will show results that can't be compared because each interface is not equally precise).
The rest of perceived audio quality besides those objective things is then highly subjective and mostly irrelevant in many situations, and as I mentioned, the differences are (objectively regarded) pretty small when the comparisons are being made properly volume-matched (which cannot be done by ear) with most gear.
My main point of this thread is just to get an overview of various source/audio devices' unloaded and loaded frequency response measurements (also to get an idea of their output impedance and behavior with critical multi-driver in-ears).
So with that being said, I invite you guys to join the party and to post your or link others' RMAA measurement plots of audio devices (though I fear that there are not many Head-Fiers who do so, as of all users I only know that @ClieOS and @shigzeo (the latter with a super precise pro interface) are doing RMAA tests).
