After writing about very high resolution measurements with the E1DA Cosmos ADC last week and touching on basically "state of the art" fidelity like the Topping D90SE, for this week's post, I thought it would be good to talk about something more "fundamental". Often spoken of among audiophile tweakers but rarely have I seen evidence of actual value/effect for many of these devices.
Before I begin with this post or even show you anything, let me just say that I do not believe audiophiles need USB isolation for use with devices like DACs unless you know you have noise issues. I think we've all see indiscriminate suggestions that audiophiles need all kinds of noise filters and isolators (like this, or this). Sometimes these things cost quite a significant chunk of change compared to the downstream device (like DAC) itself!
Over the years, I have tried out a number of USB DACs with computers and simple streamer devices like the Raspberry Pi. With a normal set-up, I cannot say I have ever heard an issue with any of the various decent DACs I've tried. Likewise, measurements already suggest that in general there are no major noise issues with at least reasonable modern devices.
However, there are times when the system is complex enough where indeed you do see ground loops and noise like the 8kHz USB PHY noise pop through. A couple months back, I showed you some of this when we took the rather useless AudioQuest JitterBug FMJ for a spin in some of these situations! Today, let's look at the effect of that little inexpensive Nobsound ADuM4160 USB Isolator (typically can be purchased for <US$25) you see in the picture above.
This device uses the Analog Devices ADuM4160 "Full/Low Speed USB Digital Isolator", see that linked datasheet for full details. Notice that although this is USB2.0 compatible, speed is limited to 1.5Mbps or 12Mbps which means that if we connect a DAC to this, we are limited to 24/96 stereo playback (USB Audio Class 1 fallback for most modern DACs). Remember this limitation and only proceed if you can accept this for whatever purpose you might have.
|Note the Linear Audio AutoRanger not being used.|
|"Mechanized Microcosm" - saw this image while surfing and traced it to this artist, cool stuff!|