The real TAPE EMULATION circuit

[Kingston]

[quote author="maxwall"]I don't consider emulation progress its simply a shift in the nature of manufacturing for corporate bottom line cost accounting vs profit. That is something you can carve in stone. Did analog tape emulate anything ?[/quote]

Analog tape was concieved with simple lack of alternatives, as the need to capture sound as clean as possible (in that sense it does emulate something). Similarly compressors and EQs were concieved to help in that fight. They were all realised as tools in sound craftmanship much later.

When it comes to corporate evils, did you consider some people (like me) are simply pathologically curious gits who enjoy challenges like this?

[quote author="maxwall"]It should not be based on a software core though. None of these dependencies on upgrade after upgrade. Like software based junk.[/quote]

Again, to some, software is just a mathematical challenge, and not everybody sees it as junk. I'd say most people embrace the ease of use since it strips off a few physical constraints (while creating the same amount of mathematical ones).

Nevermind me musing about this. I just don't like these purist black and white distinctions, as they tell so little of the big picture.

 

[chrissugar]

Just a little update.
Last week I bought a REVOX B77 MKII in very good condition for cheap. My intention is to transform it into a tape delay, but before, I will make some experiments for the tape emulation circuit.
Will try to put the rec/playback heads together and make some tests. Also will try some real magnetic tape between the heads (AMPEX456) to close the magnetic circuit with tape.

chrissugar

 

[chester]

The question for me is, what makes a typical tape sound for you ?
The distortion/compression effect ? The noise ? Tell me what you like so
much on tape.

greets

 

[redear]

Any news about this chrissugar?

 

[Fredrik]

I found some of these threads concerning the subject of tape saturation and found them interesting so I thought I would bump to see if any new inputs on this would come up.

I had some thoughts on how big part the actual tape has if one would try to emulate a similar sound. To me there is a huge difference betwen different taperecorders and the way the saturation sound, this must be in the recorder it self as i understand. If I for example overload a fostex e22 and a studer a80 1/2" machines with the same tape that would give
very different results.

There are also some aspects of the sound that is not desirable to emulate
that has to do with the tape itself such as hiss etc. in my oppinion.

I liked the idea of a overloading a transformer to get something similar perhaps with pre/de emphesis to try to tailor the sound to ones liking.

How could this be done practicaly? With a line amp > filter > transformer > filter type thing?

 

[bcaust]

[quote author="Kingston"]I'm sorry to deviate this thread slightly to the digital side of things, but I have some experience in the field, and would like to offer some insight, and at the same time recap (pun intended) the thread this far. The whole thing is written with the "tape as an effect" mentality. Sorry if you don't like it.



1. I/O electronics.

This is the least important bit in the overall sound, but it order to drive those heads a basic gain and attenuation is needed. This is the easiest thing for us to replicate as there's a choice of multitudes of good line amps. In digital form this type of gain staging hasn't been emulated as of yet, and that's what a soon to be released plugin of mine will do. I've christened the effect as intra-modulation (IM) and it somewhat captures the interaction between transformers and gain stages of electronics, and several other secondary effects that go nicely "wrong" in any analogue circuit.

2. pre-emphasis/de-emphasis.

Exteremely important factor in the saturation performance and should not be omitted. Also easy to replicate in either digital or analog form. What's your favourite emphasis curves? Simply DIY that or similarly do a digital oversampled filter using the same curves. This is the only place where impulses of the real units would do any good (and even then only if sampled at both stages, which would be difficult). Dynamic convolution is only good to recapture the filtering performance, and it might as well be done algorithmically instead (cheaper DSP wise, and easier). This was done in the voxengo TapeBus mentioned earlier in this thread, and it features, for example, Studer B67 impulses by yours truly. Its sound still leaves a lot to be desired.

3. Magnetisation.

There's very little info on how to do this digitally, and I'm doing research on the subject as we speak. Electronically one might as well do the portico thing and use real tape heads if one is willing to gut working units. If any of you manages to do this, I would be very interested in any kind of analytical measurements on it. Basically one could emulate this as a waveshaper in digital form, but the actual response curves and shapes are unavailable in a pure magnetisation form. The saturation dynamic curves are always expressed in conjunction with the tape media curves, unfortunately. Maybe one of you would have data already available?

4. Tape media.

Generally when tapes are emulated magnetisation and tape media characteristics are filed under "saturation". This is a mistake, since both play nearly equal role in tape sound. Tape media is most likely impossible to emulate electronically unless using tape loops, but that creates the many problems already covered earlier in this thread. Digital implementation is another thing. I'm doing research on this subject as well.

Basically the media has little influence on the sound when it's not driven (well, it does a little actually). Things change drastically when the tape is stressed, and we start to hear all the good sounding fluctuations that now get exaggerated. Using a separate digital waveshaper with time-based randomisation chanracteristics should work. The model should be dynamic, ie high saturation exaggerates the "smear" while quiet sounds get very little of it.. Problems arise when determining the "right" fluctuations as it varies from tape manufacturer to another. Data on this is mostly unavailable, as it's time based and difficult to measure.

5. (concerning only digital implementation)

Analogue electronics produce lots of secondary side effects: thermal coupling, physical limits of transistors/diodes etc. While it isn't anything to worry about when DIYing a tape effect, it has to be modelled separately in a digital form. I already mentioned IM, and since these effects are minor in the tape sound, IM is perfectly adequate to model them.


What did I miss?

*passes the baton*[/quote]


I suspect that the bias oscillator and bias trap may also have some effect.
Emulation may be nasty however, as it would interact with digital system oversampling etc.. On the other hand, actual tape transferred back to digital must have the same problem. Wonder what effect a high freq bias would have on a transformer. (Followed by trapping filter).

regards Brian C

 

[chrissugar]

[quote author="bcaust"]
I suspect that the bias oscillator and bias trap may also have some effect.
Emulation may be nasty however, as it would interact with digital system oversampling etc.. [/quote]

Why do you think this? :?

chrissugar

 

[bcaust]

[/quote]

Why do you think this? :?

chrissugar[/quote]


Probably because I'm not a tech. or codesmith. Just thought that bias osc & trapping filter must be doing things to heads (trannys) at high freq (ringing etc) and would probably cause some artifacts in digital. Just my 2c
--if I'm on the wrong track please ignore.

regards bc

 

[damiafix]

In the last few month was thinking more and more about a project.

A tape recorder emulation circuit.

I thought about building a complete high quality tape recorder electronics with all the correct equalisation caracteristics of the recording and playback electronics.

One method would be to use a transformer as a record/playback head with the correct inductance/impedance like in a real recorder.
The other method would be to use two real heads, and to couple them magnetically.

Yesterday I read at Prosoundweb a report about the Rupert Neve's new Legendary Audio "Masterpiece" Analog Mastering System.
The guy who tested it said that the thing really does what it say.
http://recforums.prosoundweb.com/index.php/t/4767/0
Here is the complete unit:
http://www.legendaryaudio.com/index.htm
You can download the pdf from:
http://www.legendaryaudio.com/MasterpceBro.pdf
It is mentioned that the tape emulation unit use a real magnetical circuit, but do not give more details if it is a transformer or two heads.

This made me think that this is a viable thing and it would be intersting to do some experiments.
I'm mostly interested to build something similar because I would like to have it as an aditional option in the mastering process (and why not tracking)
I supose it is not a simple thing but it can be done. Also I think that because there is no tape involved, the premagnetisation electronics is not needed.

So my questions would be adressed to the tape recorder Gurus. What impedances/inductances are common for some of the high quality tape recorders. I remenber that I found on the net a table with lots of data for various heads, but now I don't know where it is.
Also at what level heads start to saturate?
What electronics do you recomend for this project. I was thinking about some old tube Studer electronics. Any sugestions? Any schematics?
Also, do you think it is possible to emulate the two head assembly with a transformer with the right magnetic material and the right impedances/inductances?
It would be necessary to have a small gap to emulate it as close as possible?

Lets do some brainstorming.

chrissugar

This is the new link for download the pdf http://www.legendaryaudio.com/images/MasterpceBro.pdf

REgards, Damiano

 

[Kamel]

Hi all
yesterday, i tried in a big studio that bizar machine, and there is two incredible point, the first one is about the word clock, better than some well known in the business :shock:
the second point for the 3 enhanced buttons,
Triode, warmth saturation until 4, harsh and rock'n roll above
pentode, really subtlle, all along the range
Tape, tape as we can love it

of course, converter are really good, and dithering really smooth.....

big impression for the quality of this machine..

and i won nothing to write that

http://www.cranesong.com/products/hedd/

 

[12afael]

a friend of mine built a tape simulator using an old technics deck and two heads , he say he spend some ours aligning the heads for a good sound. the record head is just a resistor in serie with the head, just like a cd to tape adaptator. I don`t know if it sound very close to the tape sound (it don`t have hiss) what can I say is that I was amazed, the deck have two vu meters when they where in "red" the sound was full of life. I want one!

what I`m thinking is add a balanced input (zero field transformer maybe), two or four heads switchable for more or less crossover, maybe add a couple of switchable emphasis/de-emphasis, maybe a bias generator, a hiss source, led meters and a balanced output.

I still have some doubts:
where can I find emphasis/de-emphasis filters for diferent isp?
the bias is just for the tape isn`t?


I don`t know if this will be a temporary GAS or finally I`m going to build something.

cheers
Rafael

 

[Ego Tripper]

Sorry to dredge up an old thread, but there's little I can contributed that hasn't been covered already and I figured some people might be as curious as bcaust was about this:

Just thought that bias osc & trapping filter must be doing things to heads (trannys) at high freq (ringing etc) and would probably cause some artifacts in digital.

regards bc

Well, I've been reading a lot about tape recording lately (I just bought a 2-track and am waiting for tape & a pinch roller) and this comes from the manual for my TASCAM 32:

Where did the 150 kHz go? It disappears from the output because the head gap is too large to play it back. The individual changes of magnetic energy on the tape are smaller than the gap size so a plus and minus wave are both within the gap at the same time. They cancel out.

This would seem to suggest that the repro head is at a different distance from the tape in relation to the record head if the bias frequency can make it from the record head to the tape but apparently not from the tape to the repro head??

I would think that they would have to be at the same height for proper playback, but I have yet to conduct a head alignment, so maybe somebody else could weigh in on this?

And for those who haven't heard open reel tape (I'm fairly new to it myself), I feel compelled to answer chester's question:

The question for me is, what makes a typical tape sound for you ?
The distortion/compression effect ? The noise ? Tell me what you like so
much on tape.

First off: the noise? Definitely not. If there was a way to record with tape without the noise, I would jump right on it. In fact, I'm thinking of getting or making a noise reduction unit.

The distortion/compression effect? Simply put, yes. But that's oversimplifying things. When I first started looking for tape machines, I was looking for ways to add analog distortion and compression to my largely digital setup. I was planning on slamming the tape and getting a great hard rock sound. But then I heard what made me run out and buy a tape machine this week. My professor played a symphonic recording he made on his Nagra 4S. Now, this guy is a stereo purist-- a pair of 414s > recorder, period. And I've heard tons of his digital recordings so I have a real good feel for how his orchestral material sounds. But this tape recording, with no signal processing to interfere, perfectly showcased what tape is best at: it lifts and separates, like a bra for audio. If I had to guess, I'd say this is a result of the compression (the lift) and the distortion harmonics particular to tape (the separation). The net effect is that the entire mix is very clear, but the loud portions jump right out at you with startling life, even though we know tape doesn't have the greatest dynamic range.

 

[alexc]

> it lifts and separates, like a bra for audio



What everyone needs!

 

[mjk]

"...the repro head is at a different distance from the tape in relation to the record head..."

I think it just means that the record head gap needs to be short enough, i.e. between the pole pieces, to print the bias frequency at some given tape speed.

"But this tape recording, with no signal processing to interfere, perfectly showcased what tape is best at: it lifts and separates, like a bra for audio."

YYYEEEEESSSSS! That really comes close to how I perceive it. All analog actually but tube amplification and tape in particular.

Cheers,

Michael

 

[bobschwenkler]

Just thought that bias osc & trapping filter must be doing things to heads (trannys) at high freq (ringing etc) and would probably cause some artifacts in digital.

FWIW, the bias voltage in the machines I work on (and probably most others) is really large compared to normal signal voltages. I don't know what this translates to in terms of magnetic head response, but it might mean something.

Also, not that two magnetic heads and no tape couldn't sound good or similar to the system that is a tape machine with tape, but I couldn't imagine that the remanence and hysteresis, and other properties of the tape itself don't have a very significant effect on the reproduced sound.