Modern, musical, magical.

Also available as a part of Flow^® Mixing Suite, Flow^® Mastering Suite and Flow^® Complete Suite.

This plug-in is the product of our quest to discover where the magic of the mythological 670 hardware lies – and distil it. Modern, musical, and that special kind of magical, Bus Processor 670 delivers the unmistakable weight and warmth of the original. Plus, added saturation control, spatialization, and sidechain features for a flexible, modern workflow.  

Finally, this rare, sought-after, and expensive dual-channel variable-mu tube compressor has transcended its original form so it can transform your mix or master. Simsalabim. 

Magic Bus 

Pricey and prized, fewer than a thousand 670s were ever made, and it was originally used as a mastering limiter for vinyl. With a characteristic vibe heard from Motown to Abbey Road, the unit is known for adding sound and harmonic distortion even when you don’t do a thing. If you push it, it gives pump but – at its more subtle settings – the 670 is great for gluing things together in a warm, musical way. You can see why it’s useful on everything from the mix bus to drums, vocals, and electric guitars, and has earned its place in top studios worldwide.  

What’s cool about variable-mu? 

Variable-mu compression uses tubes to alter gain, and the compression ratio changes dynamically in response to the signal level. The result is the harmonically rich and musical compression that has made the original 670 legendary. This style of vintage processing is great for gluing things together with analog warmth and cohesion, making it ideal for mastering as well as mixing.

New Magic 

To create our Bus Processor 670 plug-in, we took the finest elements of the original and added our own wouldn’t-it-be-cool-if ideas to make a totally unique tone machine. Starting with full control of saturation points with dedicated knobs for tube and transformer saturation, and a calibration knob to influence the unique compression-dependent saturation of the variable-mu architecture. We also included sidechain options that give you control over filters, tone shift and mono/stereo linking, as well as separate outputs for M/S channels. Then there are the new spatialization features that include air band, mono maker, and stereo widening knob.  

Full-featured but dead-simple to use, Bus Processor 670 lets you find the magical sound of the 670 for yourself, with a workflow fit for your modern studio. 

The Art of Rock & Roll Science

Our reputation for producing tools that improve workflow and offer the highest quality sound is rock solid—and long. We have forged strong partnerships with premium brands like Tube-Tech, Weiss, Chandler Limited, and Marshall. Partnerships that have lasted twenty years.

This is the legacy Bus Processor 670 is built on. One of creativity, passion, and attention to detail. To create tools that innovate, you have to have heart, soul, and Rock & Roll Science.

In short

• A dual-channel variable-mu tube compressor  

• The essence of the legendary 670, distilled and made modern  

• Unmistakably weighty and warm – just like the original hardware  

• Added modern features, like saturation controls and spatialization features   

• Enhanced workflow for modern engineering and production processes   

• Console 1-ready: compatible with our mixing system hardware  

• Flow® Studio-ready: compatible with our Flow Studio hardware  

• Included in Flow® Mixing, Mastering & Complete Suite subscriptions 

• Manual

This product supports Extended Features

We love VU meters, Bakelite knobs, and analog quirks. But we want modern precision and workflow. The answer? Softube Extended Features. Easy-access panels with the innovations you need close at hand.