Empirical Audio Short Block USB filter
The Short Block is a USB cable filter that plugs in-line with the USB cable from your computer to your USB interface (either a USB converter or USB DAC). The Short Block is usually plugged into the USB DAC or USB converter and then the USB cable plugged into it. The purpose of the Short-Block is to improve audio quality by reducing jitter caused by common-mode noise on the USB cable.
Common-mode noise is voltage that develops on both of the differential signal lines in the USB cable. Ideally, this voltage would never be present or be fully rejected by the receiver USB interface, but in real systems with multiple grounds and imperfect USB drivers and receivers the noise is usually present and impacts audio quality. The Short Block reduces this common-mode noise, primarily at high-frequencies. If you have power-line hum in your system, it will generally not fix this.
The Short Block severs the +5V wire in the USB cable, so devices that rely on the +5V power in the USB cable cannot use the Short Block. The Short Block does not work reliably with the Off-Ramp 3, but works well with recent Overdrives, Off-Ramp 4 and Off-Ramp 5.
The Short block is a passive device, so it requires no power. The only requirement when using the Short Block is that the AC power for the computer of the system and the USB interface device (either USB converter or USB DAC) be source from the same AC circuit. This means using the same outlet or string of outlets from the AC panel. This minimizes the common-mode noise by itself and prevents potentially damaging voltages from being developed between the computer and the USB interface when the Short Block is installed.
The difference with the Short-Block is usually not subtle. It will take a soundstage that is relatively flat in depth and improve the depth and imaging significantly. A much more 3D presentation.
"Across the board improvements in imaging, but particularly in image height. Width is also improved, particularly the specificity of images beyond the width of the speakers."
“What I noticed is that with the Short-Block, the soundstage appeared larger; it was as if I was sitting a few rows back from the stage as opposed to half way back. Further, on some of the more 'ambient' tracks (Alan Parsons) the children sounds appeared more three dimensional”
“The SB cleans the presentation in a way that's hard to otherwise come by ... I hear a more finely resolved ambient presentation that gives the music a quieter spatial quality”
“The sound stage is larger, some that will use the term 3-D or bigger-bolder most noted in height and depth front-back. Instruments do take on a bit more impact in some cases such as the strike of a drum will be more dynamic/hard hitting/heft of tonal sound, or the strike of a cymbal will take on more impact/crash/fullness of that cymbal.”
The Short block is NOT compatible with the following USB interfaces:
- Rega DAC
- Off-Ramp 3
- Berkeley Alpha USB converter
- Anything using XMOS interface