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Question about Digital vs. Analog



 
 
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  #11  
Old February 10th 19, 10:04 PM posted to rec.audio.pro
Robert Orban[_3_]
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Default Question about Digital vs. Analog

In article >,
says...

>
>The problem with clipping in the digital domain is that the resulting
>square wave has harmonics all the way up to the sampling rate. That
>can't happen with analogue clipping, because the lowpass input filter
>will guarantee that they are suppressed well before the Nyquist rate.
>
>Those harmonics surrounding the sampling rate alias back into the
>audio band following decimation. They are nasty. Never ever allow
>digital domain clipping.
>
>d


You can clip in the digital domain, but it's difficult. It requires
oversampling the clipper, and aliasing decreases quite slowly as sample rate
increases.

Current Optimod processors use a combination of oversampling and other
tricks to get an equivalent sample rate of about 10 MHz for "clipper-like"
processes. At that frequency, aliasing distortion into the audio band is
negligible compared to the desired clipping distortion (i.e. distortion that
is equivalent to that produced by an analog clipper with the same
input/output gain shape).

--Bob Orban

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  #12  
Old February 10th 19, 10:48 PM posted to rec.audio.pro
Don Pearce[_3_]
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Posts: 2,250
Default Question about Digital vs. Analog

On Sun, 10 Feb 2019 13:04:31 -0800, Robert Orban >
wrote:

>In article >,
>says...
>
>>
>>The problem with clipping in the digital domain is that the resulting
>>square wave has harmonics all the way up to the sampling rate. That
>>can't happen with analogue clipping, because the lowpass input filter
>>will guarantee that they are suppressed well before the Nyquist rate.
>>
>>Those harmonics surrounding the sampling rate alias back into the
>>audio band following decimation. They are nasty. Never ever allow
>>digital domain clipping.
>>
>>d

>
>You can clip in the digital domain, but it's difficult. It requires
>oversampling the clipper, and aliasing decreases quite slowly as sample rate
>increases.
>
>Current Optimod processors use a combination of oversampling and other
>tricks to get an equivalent sample rate of about 10 MHz for "clipper-like"
>processes. At that frequency, aliasing distortion into the audio band is
>negligible compared to the desired clipping distortion (i.e. distortion that
>is equivalent to that produced by an analog clipper with the same
>input/output gain shape).
>
>--Bob Orban


OK, I think I've got that. I'll work it out later in Mathcad. But what
we are talking about here is accidental clipping by simply hitting
digital max. That can never be good news.

d
  #13  
Old February 11th 19, 02:56 AM posted to rec.audio.pro
geoff
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Posts: 1,386
Default Question about Digital vs. Analog

On 11/02/2019 8:28 AM, James Price wrote:

>
> I was under the impression that the primary difference is that overloading
> the front end of the ADC would potentially produce digital hard clipping at
> the output, that is assuming the amp sim's volume isn't set particularly low
> and the input level is cranked high enough. For example, a 50 dB boost applied
> to the input of an ADC vs. an analog amp. Both will clip, but my presumption
> was that the ADC would produce digital hard clipping in the form of a square
> waveform, whereas hard clipping in the analog amp would produce a waveform
> that wasn't chopped.
>


That would depend on the ADC involved and/or the analogue circuitry
before it.

I've never thought of the idea of using an ADC itself as a fuzz box. Try
it, but don't expect it to apply to any other ADC in a effect box or
audio computer interface model other than the one you've tried.

Myself, I get more pleasure out of fiddling with a guitar amp itself,
even over fuzz-boxes/distortion-pedals/whatever.

geoff
  #14  
Old February 11th 19, 02:59 AM posted to rec.audio.pro
geoff
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Posts: 1,386
Default Question about Digital vs. Analog

On 11/02/2019 9:06 AM, Scott Dorsey wrote:
> James Price > wrote:
>> I was under the impression that the primary difference is that overloading
>> the front end of the ADC would potentially produce digital hard clipping at
>> the output, that is assuming the amp sim's volume isn't set particularly low
>> and the input level is cranked high enough. For example, a 50 dB boost applied
>> to the input of an ADC vs. an analog amp. Both will clip, but my presumption
>> was that the ADC would produce digital hard clipping in the form of a square
>> waveform, whereas hard clipping in the analog amp would produce a waveform
>> that wasn't chopped.

>
> Clipping is clipping. Some analogue circuits will "clip softly" which is
> to say they have a little gain reduction right before they come to the
> clipping point. Some analogue circuits will overshoot when they clip.
> Some will get stuck for a cycle or two when they clip.
>
> All of these will result in a different spectrum. You'll still get the
> odd harmonics that you get from perfect clipping, but the ratio between
> them will be different and you'll get other stuff too.
>
> People that build guitar amps think a lot about behaviour of circuits
> when they clip, but most designers don't care about it because they don't
> expect people will ever clip anything. Hi-fi tube amps often use splitter
> circuits like the paraphase inverter or the see-saw, which you will never
> see in guitar amps because they behave very badly when clipped.
>
> When you go into clipping, you have left the normal operating envelope of
> the equipment, and you have become a test pilot. Don't make any assumptions
> about how anything will behave when it's clipped. If you intend on using
> clipping as an effect, try it and listen.
> --scott
>



And then there is the solid-state v. vacuum tube predominant even/odd
distortion harmonic thang, as you obliquely alluded to in your second
paragraph.

geoff

geoff
  #15  
Old February 11th 19, 03:01 AM posted to rec.audio.pro
geoff
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Default Question about Digital vs. Analog

On 11/02/2019 9:18 AM, Mike Rivers wrote:

>
> The same thing happens with an ADC, only its maximum output level isn't
> defined as a voltage, but as a binary number - the higher the voltage at
> the point along the waveform where the converter takes a "snapshot," the
> bigger the number. For a given word length, say 16 bits, the maximum
> output, or full scale, as it's called, is when all the bits are turned
> on. There isn't a 17th bit so the next successive samples that would
> exceed full scale if they could are digitized at the full scale value.
> And, yes, that means they're flat on top.
>
>


Cue Thekma. Ooops sorry ...

geoff
  #16  
Old February 11th 19, 03:49 AM posted to rec.audio.pro
Scott Dorsey
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Default Question about Digital vs. Analog

geoff > wrote:
>
>And then there is the solid-state v. vacuum tube predominant even/odd
>distortion harmonic thang, as you obliquely alluded to in your second
>paragraph.


That is a useless oversimplification which is no way correct, and it
comes from an IEEE Spectrum article in the 1980s. I wish people would
stop repeating it.

That article was talking about predominant distortion at low levels
without feedback, caused by the device characteristic itself. The
thing is, we don't actually use electronics that way. We use circuits
designed to minimize distortion using techniques like local feedback
and push-pull amplification, techniques like constant current supplies.
Once you do that, the distortion spectra all change in ways that are
not so cut and dried.

And of course, you can't generalize low level distortion to clipping.
When you clip a waveform, you generate odd harmonics. Generate enough
and you get a square wave. It doesn't matter if you do it with tubes
or transistors, in the analogue domain or the digital domain. That is
what clipping does.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #17  
Old February 11th 19, 03:55 AM posted to rec.audio.pro
geoff
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Posts: 1,386
Default Question about Digital vs. Analog

On 11/02/2019 3:49 PM, Scott Dorsey wrote:
> geoff > wrote:
>>
>> And then there is the solid-state v. vacuum tube predominant even/odd
>> distortion harmonic thang, as you obliquely alluded to in your second
>> paragraph.

>
> That is a useless oversimplification which is no way correct, and it
> comes from an IEEE Spectrum article in the 1980s. I wish people would
> stop repeating it.
>
> That article was talking about predominant distortion at low levels
> without feedback, caused by the device characteristic itself. The
> thing is, we don't actually use electronics that way. We use circuits
> designed to minimize distortion using techniques like local feedback
> and push-pull amplification, techniques like constant current supplies.
> Once you do that, the distortion spectra all change in ways that are
> not so cut and dried.
>
> And of course, you can't generalize low level distortion to clipping.
> When you clip a waveform, you generate odd harmonics. Generate enough
> and you get a square wave. It doesn't matter if you do it with tubes
> or transistors, in the analogue domain or the digital domain. That is
> what clipping does.
> --scott
>



We are talking specifically in an electric guitar context no ? Hardly an
amp designed to minimise distortion ?

So that would be why distortion from over-driving a solid-state guitar
amp (discount 'modelling amps') is just as pleasing as that from a valve
amp then - not ?

geoff
  #18  
Old February 11th 19, 04:36 PM posted to rec.audio.pro
Scott Dorsey
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Posts: 16,503
Default Question about Digital vs. Analog

geoff > wrote:
>
>We are talking specifically in an electric guitar context no ? Hardly an
>amp designed to minimise distortion ?
>
>So that would be why distortion from over-driving a solid-state guitar
>amp (discount 'modelling amps') is just as pleasing as that from a valve
>amp then - not ?


Comparing a tube amplifier and a solid state amplifier is like comparing
apples and oranges... totally different topology, totally different output
stage. Many of the differences have little to do with the devices and
everything with how they are used. An enormous amount of the coloration from
a tube amp is in the output transformer.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."
  #19  
Old February 12th 19, 12:31 AM posted to rec.audio.pro
geoff
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Posts: 1,386
Default Question about Digital vs. Analog

On 12/02/2019 4:36 AM, Scott Dorsey wrote:
> geoff > wrote:
>>
>> We are talking specifically in an electric guitar context no ? Hardly an
>> amp designed to minimise distortion ?
>>
>> So that would be why distortion from over-driving a solid-state guitar
>> amp (discount 'modelling amps') is just as pleasing as that from a valve
>> amp then - not ?

>
> Comparing a tube amplifier and a solid state amplifier is like comparing
> apples and oranges... totally different topology, totally different output
> stage. Many of the differences have little to do with the devices and
> everything with how they are used. An enormous amount of the coloration from
> a tube amp is in the output transformer.
> --scott
>



So there is no truth in the old adage that distortion products of
over-driven valves are of predominantly even order harmonics which are
pleasing to the ear, as opposed to the predominantly odd-order harmonics
that resulting from the distortion from over-driving solid-state
devices, which are considered unpleasant ?

geoff
  #20  
Old February 12th 19, 01:02 AM posted to rec.audio.pro
[email protected]
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Posts: 1,644
Default Question about Digital vs. Analog

geoff wrote: "
Cue Thekma. Ooops sorry ...

geoff "

People who have principles, and actually stand
by them, get to you that much, ehh?
 




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