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Author Topic: How digital amps work  (Read 1748 times)

Fossilshark

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How digital amps work
« on: July 02, 2016, 06:41:46 PM »
Ive played on alot of digital amps, particularly the line 6 spiders, fender mustang, and marshall (jcm? Some marshall modeling amp) and i was wondering how they work. Is there a processor in the preamp? How hard would it be to build a simple programmable amp like the mustang (it could run off arduino?). Im just a curious noob any help is appreciated

phatt

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Re: How digital amps work
« Reply #1 on: July 03, 2016, 09:08:47 AM »

I'm sure others here will be able to give you some direction;;
meantime my take on a lot of new technology is thus;

Yes In my lifetime I've seen some incredible advancements but lets not forget where it comes from.

Digital stuff simulates but somethings can't be reproduced "Exactly" like the original. Yes there are limitations. :-X :'(

""Better does not go on forever sometimes Better is actually the enemy of Good."" 8|

Sure if you drop a Digital Reverb it won't make a heck of a racket when it hits the floor but then it won't be able to do real tank slap so tuff luck if that happens to be the kind of reverb you are trying to replicate. :(
On the plus side digi Reverb can greatly enhance spatial realism if used wisely but with multi efx digi gear it's all to easy to get carried away and a lot of players use way too much effects and actually trash their sound.

A real world example of how hard it is to replicate real stuff,, Really well!!!

Some years back my wife and myself happened to be watching a TV doco on the history of musical instruments.

One particular section was showing a real world blind test of one of the greatest/biggest pipe organs in Europe (can't recall names/places now).
A group of 20 or so students were sat behind a screen and asked to listen to two identical pieces of pipe music,, one was the real organ the other was an insanely expen$ive digital reproduction of that very same organ. The game was to pick the real one,,, More than half of the students got it wrong.

It only took my ears two bars into the second segment to exclaim that the first one was the real organ.

And Of course I was Right,, My wife just stared at me and asked how I could tell as she could not hear much difference.
Easy I said; a Real pipe organ has the widest bandwidth of all musical instruments but the digital reproduction had way too much treble to be real.

So can you see the folly????   Spending a staggering fortune on the best digi gear money can buy only to find you missed,, you actually overdid it all and it becomes fake and sounds fake.  :lmao: :lmao: :lmao:

Rant over,, Phil.

galaxiex

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Re: How digital amps work
« Reply #2 on: July 03, 2016, 10:06:22 AM »
Sorry, not really an answer to your question, just an opinion piece about digital...

I was an early adopter of digital technology.
I was smitten by the Line 6 Axsys 212 modelling amp when it first came out.

I loved how it sounded... at first... It blew me away in the store and I just had to take it home.

The love affair wore off early, after playing it for about 6 months I got to a place where I just could not seem to dial in a sound I liked.  :loco

My theory is that at first listen, this stuff can sound great, (not to mention being enamored with the technology)
but after awhile the ear becomes "more critical" and it starts to sound.... I don't know....sterile/harsh/"too perfect"/etc.

To be fair, they do a great job "emulating" many different sounds, but in the end, that is what it is... an emulation.
It will NEVER sound like the real thing. At least not when you listen critically.

It's great tech if you need many different sounds in an neat easy to carry single package,
as opposed to having the floor littered with analog pedals and cables etc, to get the variety of sounds you might need in a performance.
Fun to fool around with at home too, but I will likely never buy another digital amp of any kind.
Even those ones that are analog amps with digital effects built in. They just never sound right to me.

To be fair, when the whole show (band) is going, the "digital sound" gets lost in the mix and who could really tell anyway?

It has its place, just not in my space.  ;)
Fear leads to Anger, Anger leads to Hate, Hate leads to Suffering.

incurably_optimistic

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Re: How digital amps work
« Reply #3 on: July 03, 2016, 10:21:45 AM »
and speaking of construction - yes, there's probably one or more DSP chips in the preamp . It would be REALLY hard to build it (designing the PCB for that would be a nightmare, then soldering all the SMD stuff, not even to mention programming the chips - if you don't have any experience with DSP stuff then forget it). Arduino can be used to control some parameters, but not as a sound processor.

Speaking about sound quality - I agree with Phil, I don't like the digital reproduction of analog stuff too. But if you're not trying to replicate the sound of something else, then the DSPs become more interesting - there's some things you just cannot achieve with analog stuff, like really long/infinite delays, clean pitch-shifting by an arbitrary interval, some crazy reverbs and others. And the sound quality got really good over the years.

In short - if you like the sound and possibilities of some digital amp that you mentioned, just buy it. You won't be able to replicate it unfortunately.

teemuk

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Re: How digital amps work
« Reply #4 on: July 03, 2016, 03:08:52 PM »
In practice, there aren't too many "digital" amplifiers in 100% meaning of the term. Most, inherently, require quite a lot of analog circuitry for overall assistance. You need analog circuitry for IN and OUT interfacing with CODEC chips, for multiplexing analog control information and converting it to digital form. SMPS supplies are practically analog and technically there aren't "digital" power amps either, there are even very few class-D designs that would feature digital data inputs (for internal DA conversion).

Also, since beginning many of these "digital modeling" units have exploited analog circuitry even in signal processing duties. "Hybrid" amps like Vox Valvereactor series and Peavey Vypyr series implement huge parts of their modeling with analog signal processing circuitry. "Valvereactor" is basically an analog effect processor circuit plus power amp in same package that emulates operation of a push-pull tube power amplifier. Peavey's "T-Dynamics" power amp is in many ways very similar circuit. Their Vypyr series amps even feature DA/AD loop in the signal path to produce harmonic distortion in an entirely analog circuit instead of generating it with a DSP algorithm. In last NAMM Vox announced to introduce modeling amplifiers with similar operating principle. The new Quilter power amps include an analog tube power amp emulation circuit very similar to one featured years ago in some "digital" Line 6 amplifiers. Even Roland's "Cube" series amplifiers feature analog "soft clipping" and "tube emulation" circuitry. You can't solely judge what is "digital" just by cosmetic appearance of things. Many early preamp processors - accused to sound too "digital" - in fact employed digital circuitry only for user interface and generic DSP effect chips could only produce time-based effects, like echos and reverbs. Overdrive, filters, gain-modulation, etc. was all handled by 100% analog circuits that had (digitally assisted) reconfiguring signal path / circuitry. Everything just -looked- digital.

In practice, by little bit of research you can easily find some general guidelines for what typical CODEC chips require as analog interface. Input voltage range and current should preferably be limited, there are single-ended and push-pull inputs and outputs, many CODECs recommend external analog circuitry for filtering both input and output signals to ensure optimal fidelity. etc.

Control information is, in many "digital" units, generated and read in very similar manner. (e.g. potentiometers supplied by low DC voltage potential, wiper voltages multiplexed and finally analog information converted to digital).

The actual DSP processing, and how its implemented, can vary a lot. There is a trend to belittle possibilities of digital modeling, saying it "simplifies" things too much to be realistic, but DSP algorithms of even the early mid 1990's modeling units were - in fact - quite dynamic by nature and a lot of research had been put to emulate tube amplifier performance in very realistic degree.

In practice algorithms are largely limited by memory and processing time involved. Today's digital signal processor get faster and faster, though, and optimising algorithms, data, etc. to decrease processing time, for example, forms a major part of content of all patents relating to "digital modeling" and alike.

For good readout I suggest you Google search for Jyri Pakarinen and David T. Yeh's whitepaper titled "A Revied of Digital Techniques for Modeling Vacuum-Tube Guitar Amplifiers". Matti Karjalainen has also published many interesting whitepapers like "Wave Digital Simulation of a Vacuum Tube Amplifier". This certainly IS NOT a topic one could cover in single post in an Internet forum. You can find hundreds and hundreds of pages of reading if you truly want to research the topic.


g1

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Re: How digital amps work
« Reply #5 on: July 04, 2016, 11:15:02 AM »
Here's a link to the article Teemu mentioned above:

http://www.mitpressjournals.org/doi/pdf/10.1162/comj.2009.33.2.85


gbono

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Re: How digital amps work
« Reply #6 on: July 07, 2016, 05:14:15 AM »
Texas Instruments and Analog Devices are two good sources for DSP audio processors. If you really want to explore a fascinating digital technology with both high powered DSP and flexible IO look at some of the products from Xilinx and Altera (FPGAs).

 

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