How to have a fading muffled effect?

[shnxx]

Hi! I’m still learning to use Audacity and I would like to know how can I make the muffle effect fading?

All I can do right now is to muffle the audio using Classic Filters being set to Butterworth, Lowpass, order 1 and cutoff as 750Hz, and applying it twice for better results. Then, selecting the muffled audio and applying Fade In effect.

What it does is fading in all the audio. What I would like to happen is to just fade out the effect, not the audio.
It is like, playing the muffled audio on normal volume all throughout then the muffled effect is slightly fading, little by little, as the audio plays by until it is completely gone on some specified part of the audio.

Is this possible? Any help would be much appreciated!

[steve]

Classic Filters being set to Butterworth, Lowpass, order 1 and cutoff as 750Hz, and applying it twice for better results.

That should be about the same as increasing the “order” to 2" and using it once.
Alternatively, you could use the “Low-Pass Filter” effect (set to 12 dB per octave). See: Low-Pass Filter - Audacity Manual

What I would like to happen is to just fade out the effect, not the audio.

There’s a trick to this:

1. Duplicate the track - Select the track, then “Edit menu > Duplicate (Ctrl + D)”
2. Apply the low pass filter to the upper track
3. Fade in the upper track
   4 Fade out the lower track

Optionally, you can select both tracks and “Tracks menu > Mix > Mix and Render”, though that is not necessary as the tracks will automatically be mixed when you export.

[steve]

An alternative approach is to apply this Nyquist code to the track in the Nyquist Prompt effect
(See: https://manual.audacityteam.org/man/nyquist_prompt.html)

;version 4
(setf hz 750)
(let* ((dry (pwlv 1 1 0))
       (wet (diff 1 dry)))
  (sum (mult (lowpass2 *track* 750) wet)
       (mult *track* dry)))

Or for a slightly different effect (this one is a filter that progressively moves the filter frequency down to 750 Hz)

;version 4
(setf lowhz 750)
(setf hihz (/ *sound-srate* 2))
(let ((hz (pwlv hihz 1 lowhz)))
  (lp (lp *track* hz) hz))

[shnxx]

That should be about the same as increasing the “order” to 2" and using it once.
Alternatively, you could use the “Low-Pass Filter” effect (set to 12 dB per octave). See: Low-Pass Filter - Audacity Manual

I didn’t know about the order. I’ll try it out!
I already tried “Low-Pass Filter” because it is one of the ones the came out when I was searching for the muffled effect. The “Classic Filter” gave me better results so I’ll stick with it.

There’s a trick to this:

1. Duplicate the track - Select the track, then “Edit menu > Duplicate (Ctrl + D)”
2. Apply the low pass filter to the upper track
3. Fade in the upper track
   4 Fade out the lower track

I did try this and it gave me good results. My only problem is that after using “Mix and Render”, in the middle part of the audio, because of the Fade in and Fade out effects, the volume is significantly low. You may refer to this image.
I tried amplifying that part by 1dB but it only made the low-volume part clipping.

\

;version 4
(setf lowhz 750)
(setf hihz (/ *sound-srate* 2))
(let ((hz (pwlv hihz 1 lowhz)))
  (lp (lp *track* hz) hz))

This didn’t do anything with the audio after applying it.

But this one:

;version 4
(setf hz 750)
(let* ((dry (pwlv 1 1 0))
       (wet (diff 1 dry)))
  (sum (mult (lowpass2 *track* 750) wet)
       (mult *track* dry)))

It did work but how can I reverse it? I would like to try to start from the muffled effect and finish with the original audio.
I did try reading the documentation that you linked but I was overwhelmed with the information

Thank you for your reply!!

[steve]

The “Classic Filter” gave me better results

Perhaps you used different settings.

This is the effect of a 2nd order (12dB/octave) Butterworth low-pass filter using “Classic Filter”:

and the is the effect of a 12dB/octave (2nd order) low-pass filter using “Low-Pass Filter”:

[steve]

My only problem is that after using “Mix and Render”, in the middle part of the audio, because of the Fade in and Fade out effects, the volume is significantly low.

I can’t explain that. It does not do that for me.
I would expect it to gradually get lower because the filter removes some of the audio, like this:

If you want to keep the amplitude about the same at the end, Amplify the filtered track before mixing.
So the steps are then:

1. Duplicate the track - Select the track, then “Edit menu > Duplicate (Ctrl + D)”
2. Apply the low pass filter to the upper track
3. Fade in the upper track
4. Amplify the upper track so that the level at the end is back up to the original level
   5 Fade out the lower track
5. Select both tracks
6. Mix and Render

[steve]

;version 4
(setf lowhz 750)
(setf hihz (/ *sound-srate* 2))
(let ((hz (pwlv hihz 1 lowhz)))
  (lp (lp *track* hz) hz))

This didn’t do anything with the audio after applying it.

Which version of Audacity are you using?

Try running it again, but press the “Debug” button instead of the “OK” button. After it has run it will open a “debug” window. Copy the contents of the debug window into your reply.

[steve]

But this one:

;version 4
(setf hz 750)
(let* ((dry (pwlv 1 1 0))
       (wet (diff 1 dry)))
  (sum (mult (lowpass2 *track* 750) wet)
       (mult *track* dry)))

It did work but how can I reverse it? I would like to try to start from the muffled effect and finish with the original audio.

The “dry” and “wet” need to be reversed, like this:

;version 4
(setf hz 750)
(let* ((wet (pwlv 1 1 0))
       (dry (diff 1 wet)))
  (sum (mult (lowpass2 *track* 750) wet)
       (mult *track* dry)))

[Areba21]

AKA high cut filter, low pass filter. It passes the low frequencies and cuts the high frequencies, contributing to the muffled echo. It can be done in Channel EQ inventory. The classic slope is 24dB/Oct. You can also turn the Q on the cut-off frequency for a resonant boost that sounds so good. Automate the frequency of low pass filters (or high frequency cut; I don’t remember their name).

[steve]

AKA high cut filter, low pass filter. It passes the low frequencies and cuts the high frequencies, contributing to the muffled echo. It can be done in Channel EQ inventory. The classic slope is 24dB/Oct. You can also turn the Q on the cut-off frequency for a resonant boost that sounds so good. Automate the frequency of low pass filters (or high frequency cut; I don’t remember their name).

Thanks for contributing Areba21, but that is not really relevant to the original question.

[Areba21]

AKA high cut filter, low pass filter. It passes the low frequencies and cuts the high frequencies, contributing to the muffled echo. It can be done in Channel EQ inventory. The classic slope is 24dB/Oct. You can also turn the Q on the cut-off frequency for a resonant boost that sounds so good. Automate the frequency of low pass filters (or high frequency cut; I don’t remember their name).

Thanks for contributing Areba21, but that is not really relevant to the original question.

Thanks for your guidance. I am very new to this forum and will be very careful for the next time.