AudioQuest shows on its website a few diagrams of how to use JitterBug, but the simple way of doing this is as follows. Use one in series with your USB DAC. Then use another in parallel on the same USB bus. If you can remove other devices to a second USB bus, do so and repeat, running all the devices through the JitterBugged USB inputs. I have exactly two JitterBugs to hand, and a MacBook Pro with two separate USB buses each with one USB port, and the JitterBugs stick out from either side of the keyboard now. I have a USB DAC running from the JitterBug on the right side USB, and the hard drive plugged into the JitterBug on the left side USB. I can’t test if more JitterBugs bring extra benefit (always in parallel, never in series, apparently), but I’ve been informed there is a notional limit of two devices per bus before the JitterBug stops adding any material benefit, and you are into gilding the lily. That being said, I’ve played around with these quite a lot and there could be an argument to use them as a kind of noise barrier on any spare input, use them to connect to any printers, routers, etc, and especially on USB ports on the back of NAS drives.
How good the JitterBug is does depend on the quality and contention of your USB bus (or buses) on your computer. My 2014 ninja-powerful MacBook Pro is pretty good, and even then improvement was noticeable, but drafting in a nasty old netbook that has such poor USB controller chips I use it as a source of interference for testing DACs was laughably good. No, it didn’t raise its game to the point where it would replace a Melco or a ReQuest, it didn’t even raise it to the level of the un Bugged MacBook Pro, but it got surprisingly near. And a NAS drive… much better, a seriously competitive source of music: again, not a Melco (the Melco also benefitted, but again mildly so) but a definite game raiser from the £39 AudioQuest JitterBug.
So, precisely what do you get in sound terms for your £40? More realism: vocals seem less pinched and stressed, you are more able to hear the tubes sagging in a wailing guitar amp in full compression, and the sound of an acoustic guitar no longer has that sort of Ovation-guitar electro-acoustic upper mid ‘thunkiness’. It’s a bit pithy, but live sounds more ‘live’ and studio sounds more ‘lithe’. Through the JitterBug, you can begin to get a bead on why people still feel CD sounds better than computer based audio, because the JitterBug pitches the sound more in that CD-like direction. In fairness, the better the bus, the less the JitterBug seems to do to the sound, but these more natural directions in performance seem consistent in intent, just varying in degree. It’s extremely consistent in making more sense of the music and making it seem more natural, but not all USB are created equal. In fairness, the JitterBug helps level the USB playing field somewhat, too.