If there’s one thing audio enthusiasts debate more than most things, it’s noise.
Just the mention of audio ‘noise’ draws a line in the sand between so-called objectivists – for whom anything that can’t be measured doesn’t exist, and subjectivists – for whom quality is all in the hearing, so if it sounds good, it is good, measurements be damned.
To complicate things further, noise can mean different things when it comes to audio. Distortion, hum, hiss, clicks and pops are among the more common definitions, and are also the easiest to hear and measure.
Then there’s the other kind of noise, the less tangible noise that you can only ‘hear’ by subjective listening. Noise in this case potentially makes music sound more congested, compressed, less open, less refined – take your pick. Whether or not ‘noise’ is actually the cause of these perceptible but difficult-to-quantify differences is another debate entirely.
A primer on audio noise
By way of background, I was firmly in the ‘bits are bits’ camp when it came to talk of ‘noisy’ USB signals. Like many I believed that if you’re sending a digital signal from point A to point B, it either gets there, or it doesn’t, and if it doesn’t you’ll hear it. Which is to say, you’ll either hear nothing, or a jumbled, incoherent mess.
But over time, I’ve learned there’s far more than meets the eye – or ear, as it were – when it comes to audio over USB.
For one thing, the physical USB cable is prone to picking up ‘noise’ from various sources, like your PCs power supply, case or other internals. Much like an antenna, it can also pick up radio interference (from WiFi routers, cellphones and other transmitters) which, if the cable is poorly shielded, can cause all types of havoc with sensitive audio equipment. If this noise makes its way inside your DAC, it can result in your DAC getting a less-than-optimal signal to process. Hence the term ‘noisy signal’.
How that will actually affect what you end up hearing through your audio system varies greatly, depending on the different parts of the chain. You may have a particularly ‘noisy’ PC, or a crappy power supply, or your DAC may not have the ‘smarts’ to filter out any incoming noise. It could also be that your cable is poorly made, inadequately or incorrectly shielded, or too long.
It’s also important to differentiate USB signal noise from other types of audio of noise, like a ground loop (which causes an audible hum and is a rather simple fix). I’m talking about the noise that gets carried by your USB cable and, if unchecked, gets mixed in with the signal your DAC is left to convert into music. The noise that, even if you can’t hear it, is still there.
The bottom line is this: if you’re connecting your audio source to your DAC using USB, you need some form of signal ‘cleaner’. Even though it’s difficult to quantify the amount and type of noise coming down the line, so to speak, what’s indisputable is that noise is there, and without treatment, your DAC simply isn’t getting the cleanest possible signal.
Turn the page to see how the iPurifier fits into this not-so-pretty picture.