Class D amp has been improving leaps and bounce over the years. I remember in the "old days" like 2005 to 2010 or so, everyone is talking about THD numbers. Same thing can be said for the sampling rate of DACs.
But now, several of the top tier class D amps (NuPrime especially) have moved beyond those numbers. THD < 0.05 is common over a wide range of power and freq so we stop talking about it. It is no longer interesting. You can't tell the difference beyond certain low THD numbers.
Similarly for DAC, we just created the mDSD under Encore brand for $99 with 32-bit/384kHz and DSD256 decoding. Sound quality is incredible.
By the way, for amp, you want to turn up the volume and typically the best performance (the lowest THD, best dynamic) is at mid volume level.
So what's the next battle ground for class D amps if low THD is now the norm?
1) switching frequency - all the NuPrime amps now switch at > 550kHz. Why is this important? It has to do with converting the analog music into pulses with varying height. With > 10X the sampling rate of CDs, you can't tell from a class D or class A amp anymore.
2) mix of class D power stage different preamp stage to create amps with different flavours. You can't tell STA-9 from a high-end tube amp. Our French distributor told us $649 STA-9 sounded better than his 5000 Euro class A amp.
Power supply and chassis now becomes one of the deciding factor for cost. Your smart phone has more computer power than a super computer of yesterday, so believe me, we can make our class D amp sounded like anything.
3) price. Good design, very reasonable price.
By the way, the deciding factor in a DAC product is no longer the chip. Realistically, the difference between ESS9018 and ESS9010K2M is not noticeable if the rest of the design is very good. Typically in a so called entry level DAC, vendors use lower price DAC chip but what makes it sounded not so good is the preamp, jitter reduction circuit (or lack of), volume control, power supply circuit etc.
If you have a high end in-ear earphones, try the $99 Encore mDSD to decode DSD256 or 32-bit/384KHz music from your smart phone to hear what I am talking about.
Next month I will take about some innovative stuff we are doing for Omnia. One of the most important design feature is to decouple the music decoding and streaming from the CPU. This can't be done on a standard PC or smart phone. It needs propriety design on the "motherboard".
