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Transformer "Weight" & Tape "Head Bump" vs LF EQ - What's Really Happening There?
Old 1 week ago
  #1
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Transformer "Weight" & Tape "Head Bump" vs LF EQ - What's Really Happening There?

Talking about analog hardware - I'm interested in the differences between fattening low end using EQ vs using transformer coloration or analog tape head bump.

I regularly use all of the above. I hear differences in the results, but - why exactly?

I'm trying to get at the physical principles behind transformer/tape LF boost that differ from EQ LF boost and precisely how that affects the sound differently.

Talking about plug-ins - I'm also curious whether modeling plug-in designers use digital EQ to simulate the frequency response of tape/trannys or if they actually try to mimic the same principles that the HW involves.

I have limited knowledge on the subject and I don't pretend to be an EE or a programmer. I'd love to learn more from the big brains on the forum.

Thank you in advance!

Last edited by Trakworx; 1 week ago at 08:10 PM.. Reason: spelling
Old 1 week ago
  #2
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Interesting, I'd love to hear thoughts on this too
Old 1 week ago
  #3
With the tape you kinda get a combinaison of dynamic EQ + Static EQ + Exciter at different stage of the process, reacting differently to a bunch of small parameter and constantly "talking" to each other while being non linear.
So it's pretty far from a simple static EQ.
We're talking about frequency response, phase shift, impulse response, THD, added noise...
Old 1 week ago
  #4
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Quote:
Originally Posted by Saxnscratch View Post
With the tape you kinda get a combinaison of dynamic EQ + Static EQ + Exciter at different stage of the process, reacting differently to a bunch of small parameter and constantly "talking" to each other while being non linear.
So it's pretty far from a simple static EQ.
Right! That's how I experience analog tape, and to a lesser extent the better tape sims do some of that.

Quote:
Originally Posted by Saxnscratch View Post
We're talking about frequency response, phase shift, impulse response, THD, added noise...
Yes, that's about as much as I know about it. Hoping to drill down a bit more in detail if possible.



And with transformers it seems like a more static effect than tape but still different from EQ...
Old 1 week ago
  #5
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Quote:
Originally Posted by Trakworx View Post
Right! That's how I experience analog tape, and to a lesser extent the better tape sims do some of that.



Yes, that's about as much as I know about it. Hoping to drill down a bit more in detail if possible.



And with transformers it seems like a more static effect than tape but still different from EQ...
With transformers its mostly pure distortion, if it really affects the freq response in the area from 20-100Hz its mostly because of impedance mismatch (which is a typical problem from puristic gear which can react very differently depending on the gear before/after).

I have some very good explanations about the effect of tape, but only in paperform and in german only. I bet you can get some serious info in english too via google.


Even when the typical low end distortion of a transformer might sound similar to an EQ boost in that area on first listening, its completly different in approach and you never will be able tomimik one with the other. Playing around with RMAA really can help to understand whats going in a analog chain.
Old 1 week ago
  #6
https://ccrma.stanford.edu/courses/1..._recording.pdf
@JP__: I'd be interested to read the German article! Can you post it?

Last edited by FabienTDR; 1 week ago at 10:00 PM..
Old 1 week ago
  #7
This one maybe slightly disturbing

Response Curves of Analog Recorders
Old 1 week ago
  #8
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If that's disturbing let's not go anywhere near turntable cartridges...
Old 1 week ago
  #9
That would be interesting indeed! Watching a sine travel through all stages of vinyl production, and see what comes out of the consumer's amp. I think to remember Dave Hill/Crane Song dedicating a plugin to this effect.

Last edited by FabienTDR; 1 week ago at 10:19 PM..
Old 1 week ago
  #10
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Quote:
Originally Posted by FabienTDR View Post
https://ccrma.stanford.edu/courses/1..._recording.pdf
@JP__: I'd be interested to read the German article! Can you post it?
One I found online: https://www.google.de/url?sa=t&sourc...zdxaJCAvSph6yi
Old 1 week ago
  #11
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Quote:
Originally Posted by JP__ View Post
With transformers its mostly pure distortion, if it really affects the freq response in the area from 20-100Hz its mostly because of impedance mismatch (which is a typical problem from puristic gear which can react very differently depending on the gear before/after).
My experience using a lot of units with colorful transformers is that yes they do sound better/worse with certain gear patched before/after in a chain, but even when patched in a sweet spot they still add that LF weight. Just as an example - no matter where it's patched in my Focusrite Red 2 EQ always adds a lot of LF weight to the sound even in bypass and the user manual brags about that sound, attributing it to the transformers.

Quote:
Originally Posted by JP__ View Post
Even when the typical low end distortion of a transformer might sound similar to an EQ boost in that area on first listening, its completly different in approach and you never will be able tomimik one with the other. Playing around with RMAA really can help to understand whats going in a analog chain.
Interesting. Can you elaborate on your use of the word "distortion"? You mean transformers add low frequency harmonics? Subharmonics? And that's responsible for the effect?

I agree that it's completely different, which is the reason for this thread. Any more detail is appreciated!
Old 1 week ago
  #12
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Seems like the old question about frequency specific enhancing distortion from circuit paths versus static frequency amplification through equalization.

The cool thing is that the high quality high end tape machines offered the best of all worlds. You would get the head bump from tape/head/electronics interactions related to the tape speed, the tape compression characteristics of specific tape formulations, the harmonic distortion of the tape machine electronics, along with the shelving eqs that were incorporated into the tape machines. Then there is the opportunity to have transformers included if desired on the output. So those machines allowed you to really massage the low end in different ways through head bump, distortion, and eq.

There are of course also ways to put different things together in a chain to model it all (digitally or analog), but the tape machines like the Studers and ATRs..... all of those non-linear interactions...... Man.....
Old 1 week ago
  #13
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Quote:
Originally Posted by Slug1 View Post
Seems like the old question about frequency specific enhancing distortion from circuit paths versus static frequency amplification through equalization.
Yep, that is the old question I ask. Is there a trove of old answers somewhere?

Quote:
Originally Posted by Slug1 View Post
The cool thing is that the high quality high end tape machines offered the best of all worlds. You would get the head bump from tape/head/electronics interactions related to the tape speed, the tape compression characteristics of specific tape formulations, the harmonic distortion of the tape machine electronics, along with the shelving eqs that were incorporated into the tape machines. Then there is the opportunity to have transformers included if desired on the output. So those machines allowed you to really massage the low end in different ways through head bump, distortion, and eq.
That pretty much sums up why I spend so much money keeping a 40 year old ATR up and running all these years...

Quote:
Originally Posted by Slug1 View Post
There are of course also ways to put different things together in a chain to model it all (digitally or analog), but the tape machines like the Studers and ATRs..... all of those non-linear interactions...... Man.....
The various models, digital or analog, each seem to get some aspects of tape sound but I've yet to find a model that gets all aspects. I really wonder how they go about recreating something like a head bump. When you think about what causes a head bump - how would you recreate that? EQ won't cut it...
Old 1 week ago
  #14
Quote:
Originally Posted by JP__ View Post
This is an excellent overview!
Old 1 week ago
  #15
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Quote:
Originally Posted by Trakworx View Post
Yep, that is the old question I ask. Is there a trove of old answers somewhere?



That pretty much sums up why I spend so much money keeping a 40 year old ATR up and running all these years...



The various models, digital or analog, each seem to get some aspects of tape sound but I've yet to find a model that gets all aspects. I really wonder how they go about recreating something like a head bump. When you think about what causes a head bump - how would you recreate that? EQ won't cut it...
Agreed. Eq has its place, but can't capture the totality of what the tape machine 'chain' could produce as a whole. Interestingly though, related to head bump, there are 'frequency response curves' that can capture at least what the tape machine 'chain' was doing to the frequency response. But you don't really see the increased depth and as you said 'weight' that the electronics were adding. The head bump might essentially mimic a 3db increase at 50Hz with a Q=2 on an eq, but the other harmonics might be folding that up an octave or so to increase depth and weight. And as you of all people would know, people made modifications to the tape machine electronics so no two might have the same characteristics.

Although I'm not using tape, my analog chain gets me where I want to be relative to harmonics and equalization in a way that I love how it sounds. But to those working with great tape machines, I know you immensely enjoy the sound.
Old 1 week ago
  #16
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Quote:
Originally Posted by Trakworx View Post
My experience using a lot of units with colorful transformers is that yes they do sound better/worse with certain gear patched before/after in a chain, but even when patched in a sweet spot they still add that LF weight. Just as an example - no matter where it's patched in my Focusrite Red 2 EQ always adds a lot of LF weight to the sound even in bypass and the user manual brags about that sound, attributing it to the transformers.



Interesting. Can you elaborate on your use of the word "distortion"? You mean transformers add low frequency harmonics? Subharmonics? And that's responsible for the effect?

I agree that it's completely different, which is the reason for this thread. Any more detail is appreciated!
No, no subharmonics.
Yes, overtones, harmonics, saturation, distortion. While the latter might sound too negative to most ppl, I assume....
Especially the cheaper/smaller designs in fact steal real low end often, so the "resonance point" is often pushed to upper lows by them. A behaviour a lot of ppl like. API comes to mymind here, for example. The ear is maybe fooled by the overtones, so it can sound like more low end.
Measurements might help to see whats really going, but might be uselessdue to impedance changes when put out of the chain as well.

The low end behaviour is mainly about the saturation of the transformers core, so highly dependend from size and material that is used in a certain build.
But in my experience its just a part, the most obvious thought, when speaking transformer sound. High freq resonances is another one for example.
Transformers are a complex topic which very few ppl fully understand. A reason why its much easier to just judge them by ear, than by theory.

To me its a strong love/hate thing with transformers. Most of them are sounding awfully smeary to my ears (and are a big part of the sound of a certain unit), especially the cheaper designs. Cool for tracking and mixing, but not for mastering imho.
I really love the Lundahl ACs atm, quite picky when it comes to levels, with an awfull distortion behaviour. But if used right, man, what a beauty enhancement without those typical blurry lows. They are pricey, even the smallest one cost more than 300,- the pair. But you always get what you pay for, that counts for transformers even more.
Ebay is a good source collecting all kinds of different transformer design that were used in old (german broadcast) consoles. I collected a lot of them over the years, but in the end the ACs were the only ones to stay. Plus the Jensen from the Hendyamp and the Sowter from the Rockruepel.

Last edited by JP__; 1 week ago at 09:24 AM..
Old 1 week ago
  #17
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Quote:
Originally Posted by FabienTDR View Post
This is an excellent overview!
Great.
There were a big comparisson with all kinds of measurements between a M15, the ADT and Satin in the german Studio Magazin some time ago. Could be a usefull source as well. They might sell it directly I think.
Old 1 week ago
  #18
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Quote:
Originally Posted by Trakworx View Post
Just as an example - no matter where it's patched in my Focusrite Red 2 EQ always adds a lot of LF weight to the sound even in bypass and the user manual brags about that sound, attributing it to the transformers.
Trackworks, i am a sound engineer, with some electrical background.

what i can say for sure, is that-

Transformers, in electrical terms, are actually inductors.

i will not get too technical, but i will make an electrical theory approximation for you which might help.

in simple terms, an inductors value (or inductive reactance), works for AC circuitry somewhat like a variable resistor. allowing current to flow or restricting that flow,and the Inductance is Frequency dependant.

the higher the frequency, the greater the inductance, and therefore a greater restriction to electrical energy and electron flow at the higher frequencies.

in inductive circuits Current (or electron flow) laggs the voltage by up to 90 degrees.

so in actual audio terms i believe there is an attenuation of hi frequencies by transformer action, not a boosting of lows.

inductors actually have no inductive reactance to DC current flow, allowing them to pass without restriction, and offering only resistive load, but as the signal becomes AC and alternating, the inductive reactance increases as a function of frequency. the higher the frequenct the greater the inductive Reactance.

the actual equation for inductive reactance is-

XL (inductance reactance) equals 2 times pie (3.14) times Frequency (in hertz) x L.

some smart arse will probablly chime in to correct aspects i have simplified, but in laymans terms that info might help.

Buddha
Old 1 week ago
  #19
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Quote:
Originally Posted by Trakworx View Post
Talking about plug-ins -
i was pretty surprised at how well received true iron was/is...
it's pretty "generic" in terms of what it's doing.
Old 1 week ago
  #20
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Thanks JP and Buddha for the interesting info about transformers!

Inductors, yes, as far as I understand it a transformer is two inductors (coils) and the magnetic flux between the two.

And a tape head is basically just a bisected transformer where the magnetic flux across the head gap interacts with the metallic particles in the tape.

And tape's "head bump" is determined by the width of the repro head gap and the tape speed vs the frequency being reproduced.

So tape sound and transformer sound are closely related but tape includes many more variables.

And there have been plenty of bad sounding transformers and crappy tape machines made, but the few really good ones have proven themselves and withstood the test of time.

I love this stuff.
Old 1 week ago
  #21
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Quote:
Originally Posted by Trakworx View Post
Thanks JP and Buddha for the interesting info about transformers!

And a tape head is basically just a bisected transformer where the magnetic flux across the head gap interacts with the metallic particles in the tape.

So tape sound and transformer sound are closely related but tape includes many more variables.

And there have been plenty of bad sounding transformers and crappy tape machines made, but the few really good ones have proven themselves and withstood the test of time.
yes and remembering that a tape machine does the process twice.

once while recording to tape, and a reverse process when playing back, where as an inline transformer on a microphone input only processes the signal once.

when transformers and tape work together in a symbiotic design then wonderfull things happen.

i have a Studer A800 mk1 24 track, which is the version with transformers. i was amazed when i took the back off the VU meter section. the sheer number was mind boggling. i will post a shot for you.

Buddha
Old 1 week ago
  #22
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Originally Posted by Trakworx View Post
Inductors, yes, as far as I understand it a transformer is two inductors (coils) and the magnetic flux between the two.

There's an important difference though, a transformer magnetically couples to each coil, as the transformer core is shared between them. It also provides galvanic isolation.
Galvanic isolation - Wikipedia
Old 1 week ago
  #23
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Hysteresis also being a key word. The under or over-biasing of tape, or driving a transformer hard, merely pushing the signal into the realm of the non-linear.

Some artists chasing the sound of tape are really after the tone of the amplifier electronics* and/or transformers. (we once set up a 1/4" Ampex AG440 exclusively for this purpose).

*typically also the first thing to be overdriven if trying to achieve "that sound" with domestic machines.
Old 1 week ago
  #24
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Originally Posted by Adam Dempsey View Post
Hysteresis also being a key word. The under or over-biasing of tape, or driving a transformer hard, merely pushing the signal into the realm of the non-linear.
Hysteresis is something I want to learn more about. I know it's a slight lag in the magnetic response of tape and/or transformers but I don't know exactly what the audible effect is. I suspect hysteresis deserves some credit for the complex interplay of dynamics and frequency that tape imparts, and is likely the missing ingredient in most if not all tape sims.

Quote:
Originally Posted by Adam Dempsey View Post
Some artists chasing the sound of tape are really after the tone of the amplifier electronics* and/or transformers. (we once set up a 1/4" Ampex AG440 exclusively for this purpose).

*typically also the first thing to be overdriven if trying to achieve "that sound" with domestic machines.
I'm increasingly convinced that the 1 to 2dB of "limiting" I get from layback to my ATR 102 is coming from the record electronics rather than the tape because it doesn't change when I change the alignment (unless I go extreme). It's a very nice sounding analog clipper to insert last before the ADC. It seems to me that the designers at Ampex could have built in more headroom if they wanted to, and maybe they intentionally made it this way as a built in safety net to avoid over saturating the tape. Kind of analogous to the "soft clip" feature of certain ADCs from Apogee and Digi. Like they made it fool proof and I'm the fool! Just speculating...

Last edited by Trakworx; 1 week ago at 07:38 PM..
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