Distortion effects

[Gale Andrews]

[Moderator note: Topic split from: http://forum.audacityteam.org/viewtopic ... 01#p195801]

We do see requests for general distortion effects quite frequently on the forum, but we tend to direct them to either the Leveller effect, or to VST rather than to making a feature request. Perhaps some kind of "multi-fx" plug-in could fill the gap for both vocal and instrument distortion effects, though such an effect would benefit greatly from "Preview" which is not currently available for Nyquist plug-ins.

Especially if you want to make a case for a built-in distortion or wave-shaping effect (which is hardly uncommon in other apps) then more of these requests need to get onto Wiki Feature Requests. So if some one replies to your response "hey this would be cool if Audacity had this some time" it should ideally be counted as a vote, even if the post is not in the Feature Requests board of the Forum.

This is what Wiki Feature Requests has to say:

• Specialised Voice effects:
  • Basic: Change gender, Change age, Chipmunks, Zeus (11 votes)
  • Advanced formant tools: (6 votes) Professional pitch change/tune while retaining the formants, so retaining the characteristics of the original voice
  • Advanced filtering/analysis tools like Praat (1 votes)

The "Basic" request doesn't include "robots" in the text but it should do as votes for those have been included therein, unless you think they should be separate.

Do I guess the instrumental distortion requests are for fuzzbox? And what is a stompbox "effect"? "Stomp box/guitar effects" has three FR votes (but as a "real-time" effect).


Gale

[steve]

Do I guess the instrumental distortion requests are for fuzzbox? And what is a stompbox "effect"? "Stomp box/guitar effects" has three FR votes (but as a "real-time" effect).

"Stomp box" usually means either:

1. A small wooden box placed under the foot than makes a drum type sound when "stomped on".
2. Any kind of standalone portable effect that is enabled / disabled by an integral foot swithch. Typically used by guitarists, though special versions for other instruments or vocals also exist.

I presume that they mean the second of these.
There are a lot more than just "fuzzbox" effects. Boss, Danelectro and Electro-Harmonix are three well known examples of companies that have specialised in guitar "stomp" (effect) boxes, and have produced dozens of different types of effect units including: Numerous types of "overdrive" (from subtle "tube" overdrive effects to hard "metal" effects and many types between), echo, delay, chorus, flange, Tremolo, and others.

A fuzzbox is a relatively simple type of distortion, often based on "diode clipping" circuits that became popular in the '60 and early 70s. It is a very small subset of "stomp box effects".

The more common distortion effects generally include tone controls and/or other methods of shaping the sound. The effects may include delay and/or convolution effects in addition to wave shaping.

The vote count for "real time guitar effects" should be very much higher than 3 as it comes up quite regularly on the forum.

There are several specialist programs that provide real time stompbox functionality, one of the best known is Guitar Rig by Native Instruments (who also distribute a hardware foot controller). Other well known products include PodFarm (Line 6), AmpliTube (Free and commercial versions), Guitarix (Linux, open source, works with Jack), SimulAnalog and others.

The comment in the feature request does not make sense attached to "Stop box guitar effects":

- one of the most useful features of Diamond Cut 7.

Diamond Cut 7 is audio restoration software and does not include guitar effects.
Perhaps that comment should have been attached to the main feature request of "Allow real-time effects (124 votes)".

The vote count for real time effects should probably also be much higher, but we already know that it is the most popular feature request.

[steve]

I'm +1 for adding some sort of "distortion" effect in the standard Audacity effect list, but something a bit more useful than just hard clipping.

[Gale Andrews]

The vote count for "real time guitar effects" should be very much higher than 3 as it comes up quite regularly on the forum.

Unless these votes are moved to the "Adding Features" board or added directly to Wiki, they won't get counted.

At the moment I'm picking up most of the feature requests posted in the 2.x Help Forum and in the "Audacity 2.x Feedback and Reviews" board, but for requests posted anywhere else such as "All Things Audio", someone else will have to volunteer to deal with them.

From where we are now, what would be a representative vote for real time guitar effects, additional to the three current votes?

The comment in the feature request does not make sense attached to "Stop box guitar effects":

- one of the most useful features of Diamond Cut 7.

Diamond Cut 7 is audio restoration software and does not include guitar effects.

OK thanks. I didn't add the Diamond Cut reference, but I'll remove it.

Perhaps that comment should have been attached to the main feature request of "Allow real-time effects (124 votes)".

The Stomp box/guitar effects" votes are part of the 45 votes for "Should include applying effects whenever playing or recording/monitoring", and those 45 votes are part of the 124 votes for "Allow real-time effects".


Gale

[Gale Andrews]

I'm +1 for adding some sort of "distortion" effect in the standard Audacity effect list, but something a bit more useful than just hard clipping.

OK, will be added. Can you be a bit more specific, so these are distinguishable as not "real-time effects". And could they be guitar fuzz effects added after the recording?


Gale

[steve]

A guitar "fuzz" effect is basically just hard clipping. It's not a particularly nice distortion effect and quite limited. It is also better suited to analogue hardware processing as analogue hardware does not run into problems with aliasing.
Something more like a "tube overdrive" type distortion would probably be more useful and suitable for a greater range of material (including vocals and guitar).

Yes, I'm in favour of adding a distortion effect as an effect that can be applied after recording (not real time), though of course real-time processing would be nice for all effects.

[Robert J. H.]

My vote is definetly in when it comes to adding distortion effects to the built-in ones.
I've long ago would have written one by myself.
The wave shaping itself gives no problem whatsoever.
However, guitarists are somewhat conservative and they expect to get the same sound they had had 30 years ago from their 2nd hand, triple vintage tube amplifier and which they had to turn full up to get the ultimate overdrive sound that costed them half of their hearing spectrum.
In other words, the VST effects tend to be a digital emulation of a well known amplifier or effect box.
Ok, that's no issue for now. A nice basic tube emulation should be sufficient for the beginning. There always can presets be added afterwards.
Which controls should appear in the plug-in? Which ones are generally in use nowadays?

[steve]

Which controls should appear in the plug-in? Which ones are generally in use nowadays?

I would have thought that for a basic general purpose distortion effect there would need to be a minimum of:

• Distortion type:Hard Clipping / Tube Overdrive / Others to be added later
  Tone controls: Bass + Treble (could just be simple high-pass and low-pass)
  Input gain: To control the amount of "drive".
  Mix: Dry / Wet balance

[Robert J. H.]

Yes, these are just the controls I had chosen too.
When I remember right, there is a soft clipping example by RBD, that has a kind of distortion effect. It changes the curved signal gradually to a square one (depending on how much the amplitude exceeds 1). I guess that's one of the simplest effects we could include.
There is also the leveler effect which you want to transfer as a legacy "distortion" effect. I must review the C code in order to see what happens at extreme values. The distortion may be due to Audacity's internal clipping prevention or floating point rounding, I am not clear on that yet.
A tube emulation should add even harmonics, shouldn't it?
It seems that a tremendous research task lies before me, only to grasp the fundamentals of distortion and overdrive (from an "analog" point of view). It's obviously that developers don't like to share their labouriously created box emulation algorithms.

[steve]

A tube emulation should add even harmonics, shouldn't it?

Yes. I've got a Nyquist code snippet tucked away somewhere for even harmonics.

The last "broadcast limiter" by Edgar-rtf used waveshaping and could easily be adapted to produce clipping without too much aliasing - or there's a "soft clipping" effect that I wrote that should still be on the forum somewhere that could be made more severe.

"Clipping" types of distortion (such as fuzzbox effects) don't tend to work well on voice because they only distort the peaks, so you just get a nasty "crunch" on those parts and no effect on the rest, so I think that at least one of the distortion types should add distortion for all signal levels. Here's a crude example of what I mean:

Code: Select all

(setq hp 100)   ; 100 Hz
(setq lp 7)     ; 7 kHz
(setq mix 50)   ; 50%

(setq lp (* lp 1000))
(setq mix (/ mix 100.0))

(defun distort (sig)
  (sim
    (highpass2 
      (mult mix
        (sum (* (/ -0.5 pi)(peak sig ny:all))
          (lowpass8 (snd-abs sig) lp)))
      hp)
    (mult (- 1 mix) sig)))

(multichan-expand #'distort s)