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Sound-Guy 23rd July 2019 06:16 PM

Aberrant DSP SketchCassette
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SketchCassette by Aberrant DSP

Aberrant DSP really is new . . . it’s creators first came up with the idea for SketchCassette as a senior design project at their university. And I am very impressed. Their first product is a wonderful and flexible lo-fi processor that emulates several “defects” of the venerable cassette tape recorder. And can even emulate subtle effects of a professional level tape machine.

And SketchCassette is available for the meager sum of US$20!
The front panel is cute and functional - note unmarked input and output gain controls under the ladder meters. On the right are the graphics for the other two tape types.

The approach they have taken is very flexible with such tape defects as limited frequency response from tape formulations, tape wear (Age), hiss, wow and flutter and dropouts, all separately adjustable, yet with some interactions such as Age interacting with Saturation effects. Starting with the section on the left you see an image with tape types listed, Type I (Iron Oxide), Type II (Chromium Dioxide), Metal (Type IV actually), and Bypass which does not bypass the plug-in entirely, it bypasses only the filtering (frequency response) aspect of the three tape types. If you were recording back in the 70’s as I was, these tape formulations were well known, and metal tape was king by the end of the decade.
Examples of frequency response for each tape type, plus a Used response for Type I - note that levels were shifted to make comparison easier and are not a function of tape type.

In addition to the frequency response differences of these tape types, SketchCassette includes the effect of wear & tear - when you played cassette tapes over and over, they degraded, typically losing more and more high end. On the SketchCassette panel below the tape types you see AGE with five settings from New to Worn. I show an example of this in the plot above for the Type I tape at the Used setting. Type I is already rolling off about 9 dB at 10 kHz when brand new, but at the Used setting it's down about 24 dB at 10 kHz! And even 4 kHz is down 6 dB. Not exactly hi-fi! And the Worn setting results in even more severe degradation. There is a tremendous range of tape deterioration possible here.

And that’s only the beginning - the Hiss control brings up quite realistic tape hiss, from essentially none to far more than any tape player I ever used if you crank it to full (5 o’clock as the knobs are calibrated). This hiss is not normal white or pink noise, but shaped noise that is close to white noise above 3 kHz and below 200 Hz, except the lower three octaves are boosted about 15 dB higher than the upper three octaves.

The Saturation control interacts somewhat with Age and significantly with the input signal level (actually, the level after using any trim with the small unmarked knob under the “IN” LED ladder display). It can be set low enough as to provide only a hint of warmth, or up to serious levels (I measured 45% THD at high settings!). Playing around with it on a bass guitar track and drum bus I had more fun than I’ve had in a while!

Up to this point the effects are not uncommon and not impossible to create with EQ, a saturation plug-in and a noise generator (with another EQ), but SketchCassette makes it easy and more historically accurate. However, the remaining functions recreate some rather more difficult defects of the lowly cassette - wow & flutter and dropouts.

Wow is relatively low frequency modulation, generally defined as less than a 4 Hz ‘wobble', and flutter is a higher frequency modulation, typically 5 Hz to 10 Hz or so. These two frequency distortions can be adjusted from off to very audible levels, as well as adjusting the modulation frequencies with selection of either an even sinusoidal motion or a random variation. Wow can be adjusted from about 6 seconds per cycle to 5 cycles per second while flutter’s range is about 5 cps up to 12 cps. The magnitude of both can be varied from off to about 2% rms (which was a bit tricky to measure). By comparison, a really good pro tape deck can run 0.02% rms or better, while cassettes may be as good as 0.08%, with 0.1% or more being typical. SketchCassette covers this range and beyond which can be very useful when you need some extra “grunge”.

A really impressive emulation is dropouts, the random amplitude modulation that occurs when tape is significantly worn physically or has been exposed to some environmental stresses. Dropouts are usually fast and random in time, and SketchCassette lets you adjust the effect in “two dimensions” with depth and intensity controls interacting for a wide range of effects. With both at maximum I saw dropouts exceeding 15 dB at times. Note you can make this effect mono where it affects both channels equally, or stereo for separate dropouts on left and right channels.

There is a down-loadable user manual that describes all the controls and the factory presets, however, there is currently an issue with presets in some DAWs. This is noted in the manual, and the guys at Aberrant DSP are working on a new DAW-independent preset system , so this should be corrected soon.

Technical Details
In my test system (PC Audio Labs Rok Box PC with Windows 7, 64 Bit, 4-Core Intel i7-4770K, 3.5 GHz, and 16 GB RAM) a single instance uses about 1.8% cpu resource, a fairly heavy load though you’re not likely to need more than a few instances in a project, if you even need more than one. SketchCassette runs with zero latency, so could be used for tracking or live work, though I’m not sure I’d ever have that need!

Available for Windows: VST3 and AAX -- macOS: AU, VST3 and AAX

A really fine little emulation with a wide range of possible uses, from adding subtle analog tape effects to warm up tracks and mixes to creating havoc! One of the more fun tools I’ve tried in years. And at a ridiculous low price. No demo available yet, but if you can’t come up with US$20 immediately, start saving up.

Fabulous FX from subtle analog treatment to far-out trashy.

Great on full mixes, drum buses, bass, and any instrument tracks you want seriously degraded!

Splits out controls for different tape defect modes enabling a vast range of audio treatment.

Easy installation and authorization.

Very low cost.

Nothing really at this price and extreme flexibility.

No VST2 version yet for users of archaic DAWs.

SketchCassette does use significantly more cpu resources than your typical EQ or saturation module, but does a lot more than EQ and harmonic distortion. Compared to some other tape FX plug-ins I have, SketchCassette cpu usage is actually on the low side.

Preset system currently under development - works with some DAWs, not others at the moment. But presets are not needed to experience what SketchCassette can accomplish.