Tape emulation explained: hysteresis, wow and flutter, head bump and hiss

A tape emulation plugin tries to reproduce what happens to audio when it is recorded onto magnetic tape and played back. That is not one effect but several stacked together: a nonlinear magnetic process that distorts and compresses, a mechanical transport that never runs at perfectly steady speed, a playhead that shapes the frequency response, and the hiss of the tape itself. Good plugins split these into separate controls, and knowing which is which is most of the battle.

What the plugins model

Hysteresis: the saturation

Magnetic tape doesn't respond linearly to the signal. It "exhibit[s] a characteristic hysteresis curve, which causes unwanted distortion of the signal", and recorders add an inaudible high-frequency AC bias while recording to reduce it (Wikipedia). Sound On Sound's Hugh Robjohns explains why: with a very weak magnetising field the particles barely respond, and bias "linearises" the medium (Sound On Sound).

What is left after bias is the sound people pay for. Robjohns says tape produces "predominantly odd-order harmonic distortion", often significant third-harmonic distortion on loud low-frequency parts, and that on high-level transients tape acts "much like a steep-slope compressor". Separately, he notes that on slow tape (below 15ips) the limited high-frequency response damages transients (Sound On Sound). The open-source ChowTape plugin models this stage directly with the Jiles-Atherton model of magnetic hysteresis, and its manual calls hysteresis largely responsible for the "warm" sound associated with tape; its Drive, Saturation and Bias controls reshape that curve (ChowTape manual).

Wow and flutter: the wobble

Tape transports speed up and slow down slightly. "Wow" is the slower variation and "flutter" the faster; standards now usually measure them together, and listeners find flutter most objectionable around 4 Hz, and "scrape flutter" comes from tape stick-slipping over a head (Wikipedia). Robjohns puts rough bands on them: wow from about 0.1 to 10 Hz, flutter from 10 to 100 Hz, and scrape flutter above that. Writing in 2010, he called speed control "the biggest problem for any mechanical tape transport system" and said plugins of the time had not nailed "convincing wow and flutter" (Sound On Sound). ChowTape exposes Depth and Rate for flutter, which can sync to tape speed or song tempo, plus Variance and Drift for the random irregularities behind wow (ChowTape manual).

Head bump and playhead losses: the EQ

Tape machines also colour the frequency response. Higher tape speeds are "prone to cause head bumps, which are fluctuations in low-frequency response" (Wikipedia), and Robjohns notes a mid-range bulge that is more obvious at slower speeds (Sound On Sound). At the top end, ChowTape models "loss effects" from the spacing between playhead and tape, the playhead gap width and tape thickness, all dependent on tape speed, with the speed control quantisable to 3.75, 7.5, 15 and 30 ips (ChowTape manual). In practice, the speed switch on a tape plugin is mostly an EQ choice.

Noise: the hiss

"The granular nature of the magnetic material adds high-frequency noise to the signal, generally referred to as tape hiss", which is why noise reduction systems such as Dolby were devised (Wikipedia). Most plugins let you add, shape or switch off the hiss; ChowTape's degradation section adds noise and an envelope on it, simulating worn tape (ChowTape manual).

A few well-known plugins

How to use it

• Match levels. Most plugins get louder as you drive them; compare bypassed and active at the same level, or you will just prefer "louder".
• Drive for compression, not fuzz. On drums and bass, push input until transients round off, then back it off a touch.
• Pick speed by tone. Treat speed as low-end shaping (the head bump) and top-end roll-off, and listen on the bass.
• Keep wobble subtle on full mixes. Wow and flutter detune everything. Heavy settings are a lo-fi effect, best on a send, a pad or a loop.
• Hiss is optional. Turn noise off unless you want it as texture; it builds up fast across many tracks.

For the wider picture on harmonics, clipping and oversampling, see our saturation and distortion basics, and for whether "analog warmth" is real, our myth check.

What we think

Tape emulation earns its place in two jobs: as a gentle transient tamer on drums, bass and buses, where the soft compression and low-end bump do something an EQ and compressor take longer to set up; and as an obvious character effect, where wow, flutter, chew and hiss are the point. It is weakest as a "make it sound expensive" button on every channel. Stacked across a session, odd harmonics, hiss and pitch wobble add up to mud, and you lose the clarity digital gave you for free.

Our inference: hysteresis is the part with a published physical model behind it (ChowTape's Jiles-Atherton approach), whereas wow and flutter on a real machine are irregular mechanical faults, and back in 2010 Sound On Sound judged that plugins had not convincingly captured them. Plugins have moved on since, so treat that as history rather than a current verdict, but our view stands: judge tape plugins on their saturation and EQ first, and treat their wow and flutter as a creative effect rather than a faithful copy. We would start with the open-source ChowTape before buying anything: it exposes every stage as a separate control, which makes it the best teaching tool of the lot.

FAQ

Is tape saturation the same as tube saturation? No. Sound On Sound says tape distortion is predominantly odd-order, while simple valve circuits lean towards even-order harmonics.

What does the tape speed control do? Mostly frequency response: it moves the head bump and the high-frequency losses.

Do I need wow and flutter? Only as an effect. Real machines had it as a flaw.