Definitions
Wow is slow pitch variation, below about 4 Hz: a note that drifts gently sharp and flat over a second or two. On a turntable it comes from an off-centre record or a slightly eccentric platter; on tape, from an imperfect capstan or a reel that drags. Flutter is faster variation, from roughly 4 Hz up into the tens of Hz: a fine tremor from motor cogging, bearing noise or tape scraping across a guide. Together they are usually quoted as one figure, a percentage of the nominal speed. A good cassette deck managed around 0.1 percent; a Walkman, much more.
What they do to music
Pitch modulation on a sustained sound is chorus. Two notes that were identical are now slightly different, drifting against each other, and the ear reads that as width, movement, life. This is why a piano chord on tape shimmers where the same chord from a file sits still, and why "warm" is the word people reach for. Too much and it is seasickness; a little and it is the sound of every record made before 1985.
Recreating it
A digital player can add wow and flutter by modulating the read position of the audio with a slow random walk (wow) plus a faster, noisier one (flutter), through a fractional-delay line so the modulation is smooth. Done carelessly it sounds like a broken pitch wheel; done carefully it sounds like a deck.
MP95 does this natively for the cassette and reel machines. The cassette preset uses about 1.8 ms of wow depth and a light flutter, deliberately below the level where you would hear it as an effect and right at the level where a sustained note starts to breathe. The reel preset uses less, because a serviced reel machine is steadier than a cassette. Both are knobs on the sound desk, so you can push a track into full Walkman if that is the mood, and the analog switch bypasses everything if it is not.
The rest of the tape sound
- Saturation and drive: tape compresses softly and adds harmonics when pushed. It makes loud things rounder.
- Head bump and roll-off: a gentle lift in the low mids and a soft top. MP95's tone and sub knobs cover this.
- Hiss: the noise floor. MP95 keeps it low, because a whisper of hiss reads as tape and a lot reads as a bad copy.
Numbers
| Source | Wow & flutter (typical) |
|---|---|
| Studio reel-to-reel, serviced | 0.03–0.05 % |
| Good home cassette deck | 0.05–0.15 % |
| Portable cassette player | 0.2–0.5 % |
| Digital file | 0 % |
Zero is not always the goal. That is the whole point of a machine that lets you choose.
Frequently asked questions
Is wow and flutter a defect?
Technically, yes: it is a deviation from constant speed. Musically, a small amount is most of what people mean by tape warmth.
Can I add wow and flutter to a digital file?
Yes. MP95 renders it in real time on any file you play, with the amount on a knob, and a switch to bypass it.