I was fortunate to have own both the A18/D90. Ive used the d90 longer than the A18, So as soon switch DAC I know the difference. I prefer more extended treble and air from the A18. Soundstage more wider. D90 bass goes abit deeper. So you need choose a right gear to pair with. My 2C can compensate the extend treble and lesser sub bass. A18 more neutral in sound. D90 is more smooth in treble. (Rounded Treble) In a way..i do think the AKM DAC implemented better on A18. But that just down on my preference as I need more treble extension. A18 mids is very neutral, no bumps, same to its bass. D90 have a little lower frequency up therefore sound deeper. A18 a little more analytical due to more airy and extend treble. And neutral sound. D90 more musical due to more lower frequency and rounded off smooth treble. With that being said, the A18 is still musical in away it sounds natural and let you hear more in the sound spectrum. Both are very detailed and clean. Great separation and depth. Great clarity. Measurements 118 vs 120db / 6vrms vs 4Vrms, A18 volume threshold sound more lively due to that extra volume gain. There you go. Seriously there are no worst on both dacs. Both are excellent performer. Build i will give to A18 more heavy and substantial. Sorry not very good at audiophile terms and bad English.
The measurements of the performance of a DAC are a snapshot of how accurately the output waveform follows the input data, together with an indication of any unwanted contribution the DAC itself makes. Using the same test equipment with the same settings, so the test conditions are as near as possible to being the same when testing different devices, provides a basis for fair and objective comparison between devices and manufacturers.
There are some areas where the same test conditions cannot be repeated. Power supplies do have a potential impact on the performance of a DAC. Some use external power adaptors, others use an internal power supply; some use switched mode power supplies, others use linear power supplies; power supply voltages vary. It is just not possible to use the same power supply for every test.
Another example is how a DAC responds to a complex waveform. From the valued information in each review, I understand that the input signals used in the test procedures are pure sinusoids, synthesised by the test equipment. The transient response of a DAC to a complex, music data stream may not exactly reflect the response to a steady state sinusoid. In all fairness, it is unlikely that the differences will noticeably affect the sound quality but might contribute to the overall perception of a listener.
However, performance figures are only one side of the coin. So many variable factors can affect the listening experience when a DAC, or any other component, is connected into an audio system. The only way to make a comparison is by an A <=> B test, in the same system and under similar conditions. Any result is subjective, based on the opinion and perception of the listener. This is the other side of the coin; both are required to provide a complete picture.
As other members have reminded me, the performance of a DAC depends on the design of the whole circuit, including power supplies, and, not solely on whether the converter chip itself is manufactured by AKM, Burr-Brown, Cirrus, ESS, Wolfson, etc. In other words, the overall implementation is important.
For this reason, I much appreciate the posting from Ntrax, as it suggests to me that the Gustard A18 (sadly no longer available) would be a better match for the music I listen to than the Topping D90. Both DACs have similar performance figures but, when part of an audio system, the listening experience is different. Reports such as this have a place on this forum, rather than on other forums where the bragging rights are based on the longest list of high-end equipment in use (and the cables used to connect the pieces together, not to mention the music collection).
This, the perception of a listener, is as much about the performance of a piece of equipment as the performance figures, which provide the essential, valuable objective basis for comparison.
Both have a place but without the work done by Amir and his colleagues, we would still be in the Dark Age of Audio.
