Can someone explain to me what "Tape Saturation" or "Tape distortion" is? Example?

soma89

Well-Known Member
Hello,
I've been reading up on tape recordings and I hear the term "Tape distortion" come up quite a bit with people talking about how pleasing it sounds. I was wondering if someone can provide me with an example of what this sounds like and how it differs from other ways of recording?

Thanks a lot
 
Tape clipping sounds a lot warmer and less distorted and more compessed compared to digital clipping....just more pleasing to the ear.

Tape saturation sounds like that. it can sometimes add 'punch' and 'warmth' to recordings.
 
It may be a bit hard to describe in words, but is relatively easy to hear. What you may have read is that, is that tape distortion is usually specified at 3%, because it has to get that high before the ear can usually hear it. Mainly, this is because only the dynamics, like cymbal crashes, cannon shots, lead guitar notes etc, that peak the signal to the tape, surpass that level during recording, and in those instances the sound starts to break up, get fuzzy, or even affect the other pars of the piece. Overload is simply trying to put to much varying signal on the tape for it to accurately reproduce. In cassettes, a good deck is specified to have a maximum THD under .8 to 1% @ 400Hz. In reality, the number is dependent on the tape, and the recording level. With the best tapes, that allow more signal before saturation, and shooting for minimum distortion, levels of .3% are achievable. I shoot to record at under 1% all the time for best balance, because if you shoot for lowest distortion, the signal to noise ratio is higher.
 
Tough question to answer in just a few words. Historically, magnetic recording had a tough row to hoe. Only by tinkering and tweaking over about 50 years (and with a few genius breakthroughs) did magnetic recording arrive at what we would call high fidelity. Iron compounds just don't want to magnetize smoothly and linearly, but they can be forced to behave well enough for a good first-generation recording. German radio stations did some amazing stereo recordings during the last few years of ww2, for example.

The problems come when you try to make the signal loud enough to overcome the everpresent tape hiss, which builds up every time you make a copy, which is what happens in a modern multitrack studio recording. Every generation (a mixdown master for making LPs, for example-- it's another copy) gets noisier and the distortion that was lurking below audibility in the first generation starts to become audible.

Add in carelessness or the unforeseen (a vocalist gets excited and hits a note way harder than in rehearsal, for example) and you have a new distortion to add to the inherent distortion and the copy distortion: tape saturation. This is when the tape runs out of little magnetic particles to be magnetized. They've already been as magnetized as they're gonna get. There just ain't no more. You get a sound that's like hard amplifier clipping: lots of odd-order harmonics mitigated somewhat by a rolloff of the high frequencies plus some compression. Used carefully by a savvy engineer/producer, it adds funk/dirt/grit to the sound. Used carelessly, it just sounds bad, like careless board work sounds bad.
Zat help?
 
Hello,
I've been reading up on tape recordings and I hear the term "Tape distortion" come up quite a bit with people talking about how pleasing it sounds. I was wondering if someone can provide me with an example of what this sounds like and how it differs from other ways of recording?

Thanks a lot

An example of pleasing harmonic tape saturation/distortion. You can especially hear it on lead vocals here.
 
The distortion is of the same kind as most simple types of hifi distortion - driving the tape's magnetic medium into saturation (nonlinearity) - the input signal is no longer directly proportional to the recorded signal. AFAIK, it usually sounds just plain bad. A poster child for overmodulated recording is the old (ancient, I guess, nowadays) early hit recording by the Moody Blues called Go Now. Find a copy, give a listen to it - and all will become clear.
 
I hear a lot of tape saturation on Bob Dylan's "Joey" on the album "Desire." I only have it on LP, I don't know if a CD copy would have it as well. I assume it's present on the original tapes so remastering couldn't get rid of it. I dislike the sound of tape saturation, and I think on "Joey" it ruins what would have been a great track, especially since it destroys the normal impeccable clarity of Emmylou Harris' voice.
 
An example of pleasing harmonic tape saturation/distortion. You can especially hear it on lead vocals here.

Are you sure that's tape distortion (not that I'm disagreeing)? I've heard that same type of distortion from vocalists going through (small) PA systems at gigs.

I hear a lot of tape saturation on Bob Dylan's "Joey" on the album "Desire." I only have it on LP, I don't know if a CD copy would have it as well.

Do you mean in particular the chorus -- "Joey, Joey, king of the streets, child of clay..." ? If so, yes, it's on the CD and, yes, it sounds bad but still a noticeably smoother sounding distortion than that on the Stones track (which actually sounds much better).

Personally I think, if used deliberately, it should be used very sparingly and very selectively and in the case of the Dylan track mentioned here, it sounds more like they took their eyes off the meters than something deliberate (which, if the case, would be ironic given the man's comments about modern-day sound quality).
 
Do you mean in particular the chorus -- "Joey, Joey, king of the streets, child of clay..." ? If so, yes, it's on the CD and, yes, it sounds bad but still a noticeably smoother sounding distortion than that on the Stones track (which actually sounds much better).

Personally I think, if used deliberately, it should be used very sparingly and very selectively and in the case of the Dylan track mentioned here, it sounds more like they took their eyes off the meters than something deliberate (which, if the case, would be ironic given the man's comments about modern-day sound quality).

Yes, I think (from memory) that it's on the chorus of "Joey" where it's especially bad, and yes, I agree that the distortion on the Stones track is more "out front" and also paradoxically sounds better. I wonder if the Stones distortion isn't actually mic preamp overload - tube distortion, that track almost certainly would've been recorded with tube gear - rather than tape saturation. The Dylan is almost certainly tape saturation. I wouldn't be totally surprised if it was intentional. Dylan has experimented with lots of different approaches to recording, and definitely had a preference for lo-fi and/or sloppy musicianship at various times.
 
Yes, analog tape signals will compress if the tape begins to saturate. The test was called MOL, or Maximum Operating Level. MOL was usually at 3% THD and was given in dB above -0dB. So an example would be MOL for a particular tape could be +4dB. Recording engineers used to use this compression behavior to great effect on kick and snare drums to make them sound fat. You didn't have to worry about attack or decay times, the signal would just squish politely at the peaks.

B&O had a cool little test instrument that would single out H3, or the third harmonic for performing MOL tests. I believe they used 400Hz as their test frequency.

When a DAC receives an overload condition, there is no compression. At least not compression as it relates to analog signals. In digital conversion, if you exceed full scale it gets ugly in a hurry. It's a twos complement encoding. If you exceed a DAC word of 0111 1111 1111 1111 by one quantization step (1 bit), the signal will go full negative. Most studios recording digital are very careful not to exceed full scale. They do this with an analog limiter feeding the DAC, or they allow themselves LOTS of headroom to allow for unknown transients.
 
Here is a page with my "distortion v level" measurements for over a hundred different cassette tapes - it can give you a good indication how hard each of these tapes can be pushed.

Alex
 
Outstanding stuff, Alex. Any chance of tabulating the results in some fashion?
 
Tape clipping sounds a lot warmer and less distorted and more compessed compared to digital clipping....just more pleasing to the ear.

Tape saturation sounds like that. it can sometimes add 'punch' and 'warmth' to recordings.
"Digital" and "solid state" clipping are essentially the same thing, hard cutoff of the top and/or bottom of the waveform. Tape saturation (I've seen it also called tape compression) is much smoother, much like a vacuum tube going into saturation - waveform peaks are "smushed down" rather than suddenly cut off. It's still distortion, but doesn't have as ragged and piercing a sound as does the hard clipping of transistor and op-amp circuits.

I googled, here's an interesting example, though it's "simulator" software and not actual tape:
http://www.virsyn.de/en/E_Products/E_VTAPE/e_vtape.html
Scroll down to the "VTAPE Saturator" and listen to the mp3's. The guitar one gives you an idea of what overdriven tape sounds like - distorted, of course. But listen to the drums. More level/saturation gives it a "bigger" sound, like John Bonham of Led Zeppelin. You can believe that tape saturation and "pushing the levels" during recording of the drums was part of the sound of those Led Zeppelin albums. I hear a lot more reverb/sustain in the snare, as the saturation DOES work like compression, and brings up the background sounds in between the foreground sounds.
 
Are you sure that's tape distortion (not that I'm disagreeing)? I've heard that same type of distortion from vocalists going through (small) PA systems at gigs.
.

I'm a sound engineer myself with a keen interest to different types of distortion. I wasn't there when Stones cut this track :D but what I've gathered from my own experiments that track sounds like it was hitting hard when 1st generation of tape was rolling.

So my guess is that the distortion you hear on Mick's vocals is most likely a combination of (tube)mic-pre stage and tape overloading (tube r2r maybe?). I doubt that the engineer used limiters before hitting the tape since it doesn't sound like that to my ears, but I could be wrong of course.

In the 60's they they didn't use compressors and limiters as much as we do now (maybe just on a master bus or tracking vocals like Lennon did with a famous Fairchild 660) - the medium (tape) itself did the trick for the most part.

The example I linked was also cut to vinyl and this of course slightly emphasizes these 'artifacts' even more.

Another great sounding tape saturation track (inspired by benb's reply) is Led Zeps: Dazed and Confused. Very fat and creamy even on this low-fi video clip.

Oh how nice drumming!

T
 
Last edited:
The O/P might be getting confused at this stage so we might as well clarify what might seem to be different words for the same thing. Saturation is what happens physically on the tape -- the tape is said to be saturated when the oxide particles can take no more magnetisation. Compression and distortion are the effects that this saturation has on the music.

Compression (of the dynamic range of the music) happens when the tape starts to become saturated because, as you push the recording level up, louder parts reach a stage where they can get no louder and quieter parts of the signal continue to get louder, thus narrowing the gap between loud and quiet (think about pushing a balloon against a ceiling). This happens in any recording system, tape or otherwise, because everything has a limit.

Distortion happens to those parts of the signal that have reached the limit. This of course also happens in any recording system but it is more objectionable in digital systems because they have a hard upper limit -- a finite maximum bit value -- whereas, with analogue tape, it happes gradually (think about pushing that balloon against a foam-padded ceiling).
 
That's a very nice clarification. This is not a simple topic with just one dimension and one answer. There are inherent nonlinearities (aka distortion) in analog magnetic recording, and pushing the tape too hard gives you new nonlinearities that blossom out in several directions and have several effects. Some of them are useful if used intelligently, and some of them just plain sound bad.

I've always believed that Todd Rundgren used tape saturation to give his drum tracks that characteristic beating-on-a-trash-can sound, which, if I'm correct, is an example of artistic use of extreme tape saturation. Quick transients like snare hits don't stick around long enough to offend the ear if they're lopped off and/or distorted and the old VU meters were designed to ignore them anyway. The distortion that is audible gives the drum hits a gruff but comical aspect that Rundgren finds emotionally useful.

Aside from the explorations of intentionally gritty sound for artistic purposes, I can't see tape saturation distortion per se as pleasant . It's not like tubes doing their soft-clipping trick, with the perfuming spray of even-order harmonics to cushion the shock. To my ears tape overmodulation (ie, over-recording) gives an unpleasant mixture of odd-order harmonics and intermodulation that doesn't sound quite like anything else but sounds far more like a transistor amp clipping than it does a tube amp. Listen to the soundtrack of 2001: A Space Odyssey-- one of the Ligeti pieces features a solo blast on a piccolo, a torture test for magnetic tape, especially back in the 1960s. It sounds like the piccolo has taken up Tuvan throat singing.

Later tape formulations (notably Ampex 456 in the mid-'70s) improved to the point where pinning the meters on the mixing board simply started rolling off the highs-- the rest of the spectrum didn't start to sound truly unpleasant at any sane recording level. And by then the use of Dolby (which actually reduces some tape distortion while it reduces noise) was widespread. So yes, it depends on the tape and when it was recorded as well. Like I said, a simple-sounding question but with a multidimensional matrix of answers.

But now you know why people were driven to make those famous direct-to-disc recordings in the '70s-- LP cutting by then was a process with much lower inherent distortion than tape, and eliminating the intermediate step of recording to tape and instead recording directly to lacquer was a sonic revelation to the vinyl generation. If we had any doubts that tape was inherently "dirty", those recordings silenced them.
 
Last edited:
Don't forget print-through, where highly magnetized particles will imprint the next layer of tape. A good example is the weird pre-echo on the last part of Zeppelin's Whole Lotta Love.

It's usually not a problem for home use, but back in the day tape manufacturers would spec it.
 
As I recall, further down the rabbit hole is linearization, or pre-distortion, to counteract tape compression by introducing waveform distortion prior to recording that will be 'corrected' by tape compression upon recording and subsequent playback. I first saw it on a 3M M56 16-track machine I used in the 80s.

Another example of creative, "correct" use of tape compression is in film recording, specifically of gunshots. If you make a nice, clean, distortion-free recording of a gunshot, no-one will like it. They'll say it sounds fake. Let it clip and saturate a little (electronically and magnetically) and your producer will say, "Yeah, now that sounds like a gunshot." Primarily because most people don't actually hear real shots, but rather Hollywood recordings of shots, which are channelled thru a sound designer for maximum hype.

For me, the acid test of intermodulation distortion was chimes (like these: https://meinlpercussion.com/products/Product/PER-CHIMES/PER-CHIMES/ made from solid bar, rather than hollow tubes like porch wind chimes.) or a bell tree. Over-recording those, or having a poor-performing amp anywhere in your system would lay a swath of hash down over the music that was gruesome.

Chip
 
Back
Top Bottom