Are Sag, Squish, Swirl important ?

[Vivek]

One hears words like Sag, Squish, Swirl when reading about Tube amps.

How important are they ?

Are they desirable traits that would make SS Amps and pedals "better" if replicated ?

If so, why do very few pedals claim to replicate these traits ?

And how come there are extremely few technical studies on the Internet in these fields. No published typical waveforms, no published time constants.


This seems to be best source of sag waveshape data at the moment :
https://www.youtube.com/watch?v=gWC86zepZfo


At start of note:



Very few milliseconds later :



Superimposed :



The "Sag" implementation that I have been working on :




Blue and Teal = first few cycles at start of note
Red =  waveshape after 150ms

Schematic here:
https://www.diystompboxes.com/smfforum/index.php?topic=127688.msg1225756#msg1225756

Reference:
https://www.aikenamps.com/index.php/what-is-sag
https://www.youtube.com/watch?v=INi6lepBZt0 Using a compressor to try and emulate the compression aspect of sag
https://www.youtube.com/watch?v=sIbwgqeSqu4  Different Sag settings on a H&K Black Spirit 200 Amp
https://www.diystompboxes.com/smfforum/index.php?topic=125517.msg1195596

[Steben]

They are words but words can mean different things in different heads.
Cathode bias shift, power rail drop and low battery are different, but all are sometimes referred to as "sag".
Swirl is modulating stuff I guess?

[teemuk]

"Sag" actually has an objectively definitive technical meaning: voltage drop under current draw (and therefore we can also discuss about definite effects of it). Whereas rest of the words can mean pretty much anything depending on who you ask from.

Unfortunately the latest trend seems to be obscuring also sag to the long list of subjective tone words such as lush, bloom, gnarl, swirl, bark, fart and et cetera.   :-(

[Vivek]

Dear Teemu,

Do you have access to Sag data like Waveshapes at start and 100ms after start of note ?

If it adds something useful to the Tube sound, I'm surprised that there is very little information and measurements on it on the net.


It appears that
Some H&K Amp models have a Sag control
Origin Effects RevivalDRIVE mentions that they have implemented Sag
There are maybe 2 patents

and then radio silence on the specifics of Sag

[Mark Hammer]

"Sag" actually has an objectively definitive technical meaning: voltage drop under current draw (and therefore we can also discuss about definite effects of it). Whereas rest of the words can mean pretty much anything depending on who you ask from.

Unfortunately the latest trend seems to be obscuring also sag to the long list of subjective tone words such as lush, bloom, gnarl, swirl, bark, fart and et cetera.   :-(

A friend of mine published a book on wine-tasting terms, many of which can be equally as fuzzy, misunderstood, and misapplied as tone terms: https://www.amazon.ca/Frugal-Oenophiles-Lexicon-Tasting-Terms/dp/0968504655  I have argued for a while that it would be great to have a similar reference for  guitar-related tonal distinctions, along with reference recordings.

[Steben]

"Sag" actually has an objectively definitive technical meaning: voltage drop under current draw (and therefore we can also discuss about definite effects of it). Whereas rest of the words can mean pretty much anything depending on who you ask from.

Unfortunately the latest trend seems to be obscuring also sag to the long list of subjective tone words such as lush, bloom, gnarl, swirl, bark, fart and et cetera.   :-(

A friend of mine published a book on wine-tasting terms, many of which can be equally as fuzzy, misunderstood, and misapplied as tone terms: https://www.amazon.ca/Frugal-Oenophiles-Lexicon-Tasting-Terms/dp/0968504655  I have argued for a while that it would be great to have a similar reference for  guitar-related tonal distinctions, along with reference recordings.

I've had some years of wine tasting clubs. There is a word in Dutch - eg "mollig", in English best as "plump" I think - which is used by some, but is refuted by just about as many. SO funny. It reminds of the guitar world.

[teemuk]

Ample amount of sag will undoubtedly effect "feel" of the amp; how it reacts to picking when overdriven. You probably can't measure a single value for time constant. Look what classic amp designs do: what is the overall supply impedance and filtering capacitance...

[anotherjim]

Synesthesia is a wonderful thing.

I have an elusive bass guitar tone I call "blobby". I used to hear it only in one room of a previous home with one particular set of speakers and on only one record. I've never heard it exactly since although I can imagine it. Probably a particular compressor on the bass?
You might get a sense of it via headphones...

[PRR]

... how come there are extremely few technical studies ... ...

Oh?

https://www.amazon.com/Guitar-Amplifier-Overdrive-Ulrich-Neumann/dp/132959665X

[Vivek]

Thanks

https://books.google.ae/books?id=41gdCwAAQBAJ&pg=PA1&source=kp_read_button&hl=en&redir_esc=y

Info on sag is rather limited.

[teemuk]

... radio silence on the specifics of Sag

Well, there's not much to discuss about. Roughly put, you just insert the R and C values of the examined power supplies* to time constant equation and that gives the rest of the "missing" details. Time constants of plate, screen and preamp supply node voltages will naturally all be different, so as corresponding time constants of different amps and effects*. Ballbark values will be in millisecond range. The lower the C or R the lower the time constant will be as well.

*there may be an ordinary power supply that sag or, in some cases, a RC filter for output of peak detector / envelope follower.

But time constant gets us only so far that it's nearly useless information to us except for experiments with nothing else than a battery and RC circuit. In practice time of sagging will vary dynamically depending on magnitude of current draw (real or simulated) and input frequency. i.e. Supply voltage will sag faster at current draw of 1kHz input than at current draw of 100 Hz input. There's also great importance of how much sagging actually occurs. 2% or 20% ...? Big difference.
Recovery time, on the other hand, is dictated by slowth of the AC supply feeding the filter. It's not a battery so we have rise times of rectified sine waves at borders of our low end hearing range. Recovery is still usually faster than actual sagging.

As for time constants, note that supply with 1 ohm R and 200uF C has same time constant as supply with 100 ohm R and 20 uF C. So there may not be great difference in time constants of tube rectified supplies with low filtering capacitance versus SS rectified supplies with higher filtering capacitance. Yet, higher supply R of tube rectified supply will result to greater amount of voltage drop and more noticeable effects of headroom drop under sustained loading.

[Vivek]

Thanks Teemu

So I will just have to breadboard it and tweak and see what sounds good.

The YouTube link I posted earlier is the only source i found that showed waveshape changes over time for a real tube amps I will try and get inspiration from that starting point.

I did see some video that showed that Sag really makes the attack of a note shine out, adding more punch to the sound.

(No, I dont have definitions for "shine" and "punch")

[teemuk]

So I will just have to breadboard it and tweak and see what sounds good.

That's good design practice overall.

Basically good estimation is that sag is inaudible if it's either too fast or too slow. In between values will effect "feel"; how amp rrsponds. Yes, definitely best to listen and play in interaction.

I did see some video that showed that Sag really makes the attack of a note shine out, adding more punch to the sound.

Yes, its gradual compression (by clipping) after attack so sag emphasizes initial transient of picking. The side effect of making attack stand out is that tone turns "spongier", it caves in after that attack. Some say "tighter" amps (with lesser amounts of sag) would actually be the "punchier" ones. I guess this falls down to personal taste.

[Vivek]

Its quite easy to have a pot to dial in the amount of sag (But then the time constant also changes)

Maybe there is a reason that H&K Sag control is an 8 position rotary switch rather than a pot.