Bear in mind we are talking about upsampling a preloaded track, (eg MP3 320kb) from a lower rate to a higher rate, (eg DSD256) with the RU7 which is an algorithmic numbers game based on imperfect lossy data rather than the playback of audio tracks already natively encoded as DSD64 etc.

Whilst I agree power drain is one factor, be it native or upsampled, there is indeed a difference in the quality of the audio output through the various sampling rates. Enough to to not always want the DSD256 upsampled rate for whatever you are playing.

DSD 64 was created by Sony in late 80s and was sold as Bitstream in the 90s – aka 1-bit DAC technology. DSD 128 and 256 came later. DSD 128 is also known as DSD double data rate, as it doubles the sampling rate and DSD 256 is quad. “64” means 64x oversampling, “128” means 128x oversampling, etc.

That is a simplified comparison with PCM in terms of “Sampling rate” to make sense to consumers, the technical DSD measurement is the “frequency” of the taps – it’s measured in Mhz. For example DSD 64 = 28Mhz and DSD 128 = 5.6mhz.

So if you divide 28 million by 44,000 (CD audio) you get 64 and 5.6 million by 44,000 you get 128. That’s how they came up with the numbers.

Now, if you have a choice of course you will use DSD256 – just like you will choose a 320kb MP3 rather than a 128kb MP3. Cayin gave you a choice not because of sound differences but because of the power drain from your device, as the higher clockspeed will use more energy. Otherwise, they will just give you an off/on switch and just do all conversion to DSD 256. They need to support DSD 64 as do all DACs because most of the DSD music available are recorded in this format.

Hi Thomas, thanks for the positive feedback on the review. Unfortunately I have not heard the W4 yet but it does intrigue me long with iBasso’s new DC-Elite dongle.

Oh its not about the driver; it’s plug and play. It has more to do with the power of the USB socket, as the RU7 is quite power-intensive. Its more reliable from a powered USB hub than directly out of the installed socket, and it works just fine for OTG.

The RU7 is 400mW into a 32 ohm load, so taking that into account, you are going to get roughly 42-45mW on a 300 ohm load. The max power handling of the HD 660S2 driver is around 200mW with a sensitivity rating of 104 dB @1 kHz. What that means is that you won’t be tapping into the best of what the driver can do voltage-wise but it should have no issues with volume on the RU7 using its high gain 4.4mm balanced output.

On a subjective level the tonal match is quite nice, though a bit soft in its leading edged, even when using the DSD256 upsampling option. Still, its the best of the dongles I have reviewed to date so if you really want a dongle then this is it.

I dont have an iFi Audio DAC Signature 2 to compare it with but yes, you can use the RU7 as a DAC. It has a line out option and can take a signal from your PC or MAC and line out to a compatible amplifier.