AudioQuest JitterBug FMJ USB Data Filter

The AudioQuest JitterBug FMJ is a passive USB filter that uses two separate circuits to rid both the data lines and the 5-volt power supply of a USB port from high-frequency interference. It's plugged in between the source and the USB DAC – or simply into a free port next to it.

Why a USB noise filter?

A USB port delivers not only data, but also all the high-frequency junk that a switching power supply, processor and radio modules produce. This portion travels via ground and supply line directly into the converter, disturbing its sensitive analog section there. The JitterBug FMJ dampens exactly this range before it arrives. What you notice from that: a quieter background, less harshness in the treble, and imaging that sorts itself out better.

What you get

A thumb-sized component with a USB-A plug on one side and a USB-A socket on the other, in a sealed metal housing. Pure hardware: no driver, no app, no subscription – just plug it in.

Who is the JitterBug FMJ for – and who isn't it for?

Ideal for anyone sending music over USB from a computer, NAS or streamer into a converter – even in the car, where the USB port is rarely a model citizen. Straight talk: if you exclusively listen to vinyl, CD or radio, you don't have a USB path and so nothing to filter. And it's not meant for fast data connections – its circuit is designed for USB 2.0.

Our verdict

One of the most affordable sensible interventions in a digital chain – provided there's a USB run to calm down in the first place. We'll tell you straight whether the filter is worthwhile in your setup: HD Zürisee in Wädenswil, 044 680 22 00, WhatsApp 076 534 22 00 (text only, no calls) or shop@hdzuerisee.ch.

Technical data

• Type: passive USB noise and data filter
• Filter principle: two discrete circuits for data lines and 5V power supply
• USB standard: USB 2.0 (RF bandwidth limited to 480 Mbps)
• Connections: USB-A plug (input), USB-A socket (output)
• Housing: sealed metal housing (Full Metal Jacket) with a carbon-loaded, RF-absorbing cover
• Dimensions (W × H × D): approx. 1.8 × 0.7 × 5.0 cm
• Weight: approx. 25 g
• Use: in-line before the USB DAC or in a free port on the same bus; maximum two units per USB bus

Frequently asked questions

Where's the best place to plug in the JitterBug FMJ?

Two positions work. Either in series between the source and the USB DAC, where it filters directly in the signal path. Or into a second, free port on the same computer, where it calms the shared USB bus. Which variant brings more depends on the device – either one is switched in seconds.

Does the JitterBug work on a USB 3.0 port?

It fits mechanically, but it's a USB 2.0 filter: its circuit limits the transmitted high frequency to the 480 Mbps of the USB 2.0 standard. For audio, that's more than enough. For fast data connections – such as an external SSD in USB 3.0 mode – it doesn't belong in the line.

Can I use two JitterBugs at the same time?

Yes, but no more than two per USB bus – AudioQuest specifies that explicitly. It usually makes sense to have one in the signal path and a second in a free port. Stacking three or four eventually dampens the dynamics too. More isn't better here.

What sets the FMJ apart from the earlier JitterBug?

The housing. FMJ stands for Full Metal Jacket: the filter circuit sits inside a metal shell, plus there's a carbon-loaded, RF-absorbing cover over the socket. Both shield against interference from outside. The actual dual circuit for data and power lines has stayed the same, it just works more quietly.

Why buy the JitterBug FMJ from HD Zürisee?

Because we tell you beforehand where the filter helps and where it doesn't – on some streamers, the effect is small. We've been building digital chains for decades, know the typical sources of interference, and in Wädenswil we'll also supply the matching converter right along with it. No miracle promises.

Goes well with

At the other end of the line, ideally sits a good converter – to be found among the DACs & D/A Converters. The matching connection is under USB Cables, more small items in Accessories, and the brand's full range in the AudioQuest world.