What is scrape flutter?

Fred Thal

[Industry Expert]
Jul 15, 2016
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Please let me begin by acknowledging that there are many tape hobbyists active today. There are also many audiophiles.

But if we are defining an audiophile as someone who demands the best possible quality playback, then we might want to explore the state-of-the-art in analog tape.

Scrape flutter has been around since the dawn of analog tape. While it's easily detected and quantified with the appropriate instrumentation, many have argued (for almost fifty years!) that it's essentially inaudible in music recordings. Nothing to worry about, they say.

But is this actually the case?

I would say that relatively few people have ever experienced what an analog tape recording (and its subsequent playback) can sound like without scrape flutter.

One could rightly say that we make a big deal of scrape flutter at ATAE. And always have. We often needle the record labels and their mastering engineers who work with analog tape today, asking them why they are using high scrape flutter reproducers for the playback of important master tapes.

All that hard work to master the very best quality re-issues possible, and yet none of them are using ATAE reproducers for the original master tape playback?

We almost never get a reply to that question. Only silence.

It could be because most people do not really understand what scrape flutter is.

Or, what it does to the audio.

Or, where scrape flutter comes from.

The audio reviewer Jonathan Valin, from the Absolute Sound, recently wrote a review of a DS Audio optical phono cartridge. In that review, Jonathan reminisces about the old Decca London cartridge, nostalgically describing how the Decca's novel architecture eliminated a common source of distortion originating from the cantilever assembly found in almost any other cartridge.

Importantly, he wrote about what happens to the sound when that very familiar distortion is absent.

As I read that review from Jonathan, I kept thinking, wow, this subject of what happens when you remove cantilever haze is nearly perfectly analogous to removing the scrape flutter distortion seen in analog tape!
 

topoxforddoc

Well-Known Member
Feb 20, 2015
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Cheltenham, UK
Must be pretty hard to remove all transport/head friction, which causes the tape to stretch longitudinally.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
Must be pretty hard to remove all transport/head friction, which causes the tape to stretch longitudinally.

Substitute the word stretching with the word vibration. Now you are better understanding scrape flutter.

The science-based study of the phenomenon is in a field called tribology.
 

Tom B.

Member Sponsor
Jul 10, 2011
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I can hear scrape flutter on some recordings, but someone had to teach me what to listen for. And, it took a few hours in front of several machines to do it (think Ampex 350 as starting point). What I haven't figured out is where in the chain the artifact is originally introduced or most pronounced. Can we assume that some flutter starts with the original tape recording and is compounded when that same tape is played back for further mastering?

Has anyone quantified scrape flutter on tapes which have gone through remastering or transfer to digital?

Tom
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
Can we assume that some flutter starts with the original tape recording and is compounded when that same tape is played back for further mastering?

Yes. You have it exactly right.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
Has anyone quantified scrape flutter on tapes which have gone through remastering or transfer to digital?

That can be difficult. Perhaps you're familiar with Plangent Processes and their work in this area?

Regardless, we require a so-called technical carrier, in other words a time-base invariant pilot signal to properly do the analysis.

Unfortunately, such signals (like, for example, the latent recording bias) are normally present only in the tape reel (or copy generation) on hand. So you can't go back up the chain to pinpoint the worse offender. By the way, this is just one reason why we say analog tape replication is a lossy process.

Now, please don't hate me for sounding like a commercial here, but for many, many years ATAE has been telling the record labels and their mastering engineers that the single most responsible first step in planning any high-quality re-issue is to first listen to the original surviving master tape on a state-of-the-art reproducer that is adding absolutely no additional flutter.

That they still don't get the technical reasons for doing this is disturbing. To say the least.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
What I haven't figured out is where in the chain the artifact is originally introduced or most pronounced.

Based on my own study, I believe that it can be considerably worse in reproducing than it is in recording.

A large part of why this is so relates to headblock design.

In a typical confidence recording headblock, (having an erase, recording and reproducing head in that order) the worst scrape flutter will usually be seen at the last head, the reproducing head.

So, eliminating any scrape flutter excitation sources in the reproducer is a perfectly logical exercise, if you actually seek audiophile quality tape playback. It was a big reason for our development of our SHRO headblock designs for the Studer precision guidance transports.
 

stellavox

Well-Known Member
Apr 23, 2010
284
61
1,583
So Fred,

How do YOU "analyze" scrape flutter? By playing back a blank tape and looking at the output with a spectrum analyzer? By recording a single tone and looking at its sideband products - in the amplitude / time domain??

Then, what did YOU see and how did YOU minimize it/them? Or is this a trade secret?

Class is IN!

Charles
 

microstrip

VIP/Donor
May 30, 2010
20,806
4,698
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Portugal
So Fred,

How do YOU "analyze" scrape flutter? By playing back a blank tape and looking at the output with a spectrum analyzer? By recording a single tone and looking at its sideband products - in the amplitude / time domain??

Then, what did YOU see and how did YOU minimize it/them? Or is this a trade secret?

Class is IN!

Charles

See this past WBF thread http://www.whatsbestforum.com/showthread.php?22018-Do-different-tape-transports-sound-different&p=423990&viewfull=1#post423990
 

Tom B.

Member Sponsor
Jul 10, 2011
158
28
933
That can be difficult. Perhaps you're familiar with Plangent Processes and their work in this area?

Regardless, we require a so-called technical carrier, in other words a time-base invariant pilot signal to properly do the analysis.

Unfortunately, such signals (like, for example, the latent recording bias) are normally present only in the tape reel (or copy generation) on hand. So you can't go back up the chain to pinpoint the worse offender. By the way, this is just one reason why we say analog tape replication is a lossy process.

Now, please don't hate me for sounding like a commercial here, but for many, many years ATAE has been telling the record labels and their mastering engineers that the single most responsible first step in planning any high-quality re-issue is to first listen to the original surviving master tape on a state-of-the-art reproducer that is adding absolutely no additional flutter.

That they still don't get the technical reasons for doing this is disturbing. To say the least.

I like the comment about 'adding absolutely no additional flutter' for several reasons, some of them speculative. First, there are plenty of good original recordings where the scrape flutter is present, and we've come to accept that sound as being characteristic of that particular era. If we added additional flutter we'd probably degrade an already grainy recording. Grainy, gritty, whatever you call it, it's present on many of the older masters. At some point you'd expect a change in timbre.

Second, the flutter, which is simply heard by us as part of the audio playback (it is sound, after all) is either additive to the original flutter or further modulated along with it, resulting in an increased loss of the original signal.

Reasonable, or no? Again, If someone hadn't taught me how to 'hear' scrape flutter, I probably wouldn't think much about it. But on many recordings it is there and on occasion I do pick it out.

Tom
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
So Fred,

How do YOU "analyze" scrape flutter? By playing back a blank tape and looking at the output with a spectrum analyzer? By recording a single tone and looking at its sideband products - in the amplitude / time domain??

Then, what did YOU see and how did YOU minimize it/them? Or is this a trade secret?

Class is IN!

Charles

Hi Charles King,
Thanks for posting.
See microstrip's reply to you.
That's the thread you want to read to get started on scrape flutter measurement techniques.
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
. . . Second, the flutter, which is simply heard by us as part of the audio playback (it is sound, after all) is either additive to the original flutter or further modulated along with it, resulting in an increased loss of the original signal.

Reasonable, or no?

Yes. Absolutely reasonable.

Flutter in analog recording and playback is indeed cumulative.

If someone is making a new generation tape copy (like for example, a stereo mixdown from a multitrack original, or a new copy master for subsequent duplication) the flutter adds in every stage, becoming compounded and convolved.
 

Ron Resnick

Site Co-Owner, Administrator
Jan 24, 2015
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Thank you for starting this thread, Fred. Your expertise is greatly appreciated!
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
Scrape flutter originates not only from the tape traveling over the heads, but also from how the tape guidance through the headblock is achieved.

Ampex was the American manufacturer who believed that scrape flutter was of little consequence in analog audio reproduction.

The competing manufacturer holding a different view was Studer in Switzerland. (Unfortunately, people like to talk about Studers without distinguishing between their long list of models. That's always a mistake because those models are oftentimes very different in construction.)

Probably 99.99 percent of all recorders ever made were forced-guidance tape path designs.

The still popular Ampex ATR-102 is a forced-guidance transport, but it also has a very interesting (and very severe) forced-guidance headblock architecture. It's not that Ampex made a mistake. The extreme forced guidance in the ATR headblock is there by design. Ampex knew exactly what they were doing. They believed the resulting high scrape flutter was an acceptable trade-off for what they wanted to achieve.

The fastest way to discover what scrape flutter sounds like is to compare it to playback that lacks it.

To me, it's immediately audible.

If you want to hear a tape machine that is adding the least amount of scrape flutter, you need to find a properly working Studer A80, or it's successor, the A820. Those (and the multichannel A800) are the only two Studer models that were precision guidance transports using precision guidance headblocks.

The precision guidance Studers cost at least ten times more to construct than a forced-guidance design. This goes a long way to explaining why almost no other tape machines employed precision guidance architectures.
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
Fred,

Can you describe what scrape flutter sounds like? Perhaps an example of a sound track with and without flutter would be great. Very curious to know, so that I can listen out for it.

Thanks

Charlie
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
Fred,

Can you describe what scrape flutter sounds like? Perhaps an example of a sound track with and without flutter would be great. Very curious to know, so that I can listen out for it.

Thanks

Charlie

I presume you mean in audiophile terms?

An obscuring veil of grunge. (Can even be raspy sounding in bad cases.)

Haze. Looking through a dirty window.

And with the right instrumentation, we can clearly see that the scrape flutter is adding unwanted frequency modulation and also unwanted amplitude modulation. This can be ugly. But note that because scrape flutter is way out of the band of (is much higher in frequency than) the old-time accepted flutter measurement standards, a typical flutter meter won't even show it.

Again, possibly the very best teaching demonstration is to simply listen to the same tape, played back on a reproducer that is adding an order of magnitude lower scrape flutter. The terms that most often get mentioned by participants in such a demonstration are clarity and focus.

It's a bit of work to set up such a demonstration, if you want everything else made equal and identical, to eliminate all other variables that might be audible. But it's certainly do-able and we have done this, years ago. We used to have a page on scrape flutter on the ATAE website.
 

topoxforddoc

Well-Known Member
Feb 20, 2015
67
6
138
Cheltenham, UK
Fred,

Many thanks for the helpful reply. I think I get it. I watched a video just now about Celemony Capstan audio restoration software, and they explained normal W&F as well as scrape flutter. It had working examples, so you can hear the difference between restored and raw files with W&F. All I need is a spare Euro 3900 for the software :)

http://www.celemony.com/en/capstan

Best wishes,

Charlie
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
I should emphasize that you can't get to extremely low levels of scrape flutter by using standard recording headblocks. This is an important part of why we have told audiophiles for over twenty years that you don't ever want to use a tape recorder to play back tapes.

While the expensive precision guidance recorder-reproducers from Studer were undoubtedly very nice, the truth is that even a stock Studer A80 or A820 recording capable headblock will never let you hear what vanishingly low scrape flutter sounds like.
 

Ron Resnick

Site Co-Owner, Administrator
Jan 24, 2015
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And that, Fred, is presumably why you developed the ATAE SHRO (single head reproducer only) machine?
 

Fred Thal

[Industry Expert]
Jul 15, 2016
161
11
123
And that, Fred, is presumably why you developed the ATAE SHRO (single head reproducer only) machine?

Actually, it was one of many design goals of our Model One and Model Two reproducers.

Some of these include:

Protecting high-value master tapes from mechanical damage

Protecting high-value master tapes from unintentional erasure or overwrite

Eliminating stationary path components for improved tape protection (including tapes exhibiting soft binder syndrome)

Reducing and equalizing tape tensions seen across the headblock and at the capstan interface

Eliminating sources of scrape flutter excitation

Improving dynamic azimuth stability

Lowering flutter
 

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