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What important feature do analog tape simulators lack?

It's a strange world where you can buy a secondhand analog tape recorder for less than the price of some tape emulation plug-ins and devices. But which will give you the most authentic sound?


The early days of digital were so exciting. Suddenly you could record without discernable noise and distortion. Prior to that, an important part of the recording process was managing the vast amounts of noise and distortion produced.

And weren't those ultra-clean digital recordings sooooo good?

Err. no. They were not good. It was interesting for a time to be able to record cleanly. But after a while the novelty wore off, and the 'dirty' sound of analog became a longed-for attraction.

So we started buying old vacuum tube gear. That helped. Then plug-ins became available that would 'grungalize' our squeaky-clean digital signals.

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And then came analog tape emulators.

But what is it that analog tape emulators actually do?

Analog tape recorders produce a certain kind of distortion. It increases with higher signal levels. It is also symmetrical on positive and negative peaks in the signal, leading to the generation of strong odd-order harmonics.

A single-ended tube amplifier on the other hand is asymmetrical and produces a significant quantity of even-order harmonics.

So a tape emulator sounds different to a tube emulator (or real tubes) and adds another useful tool to the audio toolbox.

Of course, analog tape recorders were also noisy. Tape emulators generally give an option whether you have the noise or not. Believe it or not, it is sometimes useful to have it.

But there's one feature of analog tape that emulators lack. And that is wow and flutter.

One tape emulator actually says this is a good thing, to lack this intrinsic component of the analog tape sound!

Let's be clear... wow is a bad thing. Wow is a noticeable cyclic up/down change in pitch. It is truly horrible.

But flutter is another thing totally. Flutter is a fast and mostly irregular change in pitch. It's far too fast to be perceived as a pitch change. Instead it adds something wonderful to the signal...


You get sidebands with tubes. Put a clean 1 kHz sine wave into a tube amplifier and turn up the gain. You will get additional frequencies at whole-number multiples of the input frequency.

You will also get intermodulation products with more complex relationships.

But the thing is that they don't move. They are frozen and locked to the input signal.

In analog tape, not only do you get sidebands due to the distortion, you get massively more, and more complex, sidebands due to the flutter. And they change continually.

This is what gives analog tape its incredible rich, warm and involving sound.

But the emulators often miss that. So far...

By David Mellor Monday August 10, 2009

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