Suggestion (Bandpass Filter and Custom FFT Filter)

[Videogamer555]

Of the 4 main types of filters that exist, Audacity only implements 4 of them, bandstop (called Notch Filter in Audacity), highpass, and lowpass. I don't know why, but for some reason, the makers of Audacity decided to leave out the bandpass filter. I don't know much about music industry sound processing, as my hobby is related to science, not music, but signal processing for science/engineering bandpass is a VERY IMPORTANT filter. My interest in this software is for technical signal processing (not music processing). I don't know what audience this software is aimed at, but Iwith out bandpass filters, I can tell you who it's NOT aimed at. And that's science/electronics hobbyists. But since there are at least some people (me, and hopefully others too) using for science purposes, I would HOPE that the creators of this software decide to add a bandpass filter as one of its built-in filters.

Now onto the second suggestion. FFT Filter.
This would allow you to add create your own custom filter based on FFT technique. I'm thinking the dialog box for this filter should show the spectrum for the sound, and allow you draw a filter into the box that is showing this spectrum. It would be very much like the FFT Filter used in Goldwave, but unlike that one (which has frequency axis fixed at logarithmic scale, and amplitude axis fixed at dB scale), my suggested FFT Filter for Audacity would actually give you an option to set the frequency axis to either logarithmic or linear, and would also give you an option to set the amplitude scale to either dB (logarithmic) or mV (linear).

[steve]

A notch filter is a particular type of band-stop filter in which the stop band is very narrow.
http://en.wikipedia.org/wiki/Band-stop_filter

the makers of Audacity decided to leave out the bandpass filter.

You can perform band-pass filtering by applying a high-pass filter with a low corner frequency (passes the mid and high frequencies), followed by a low-pass filter with a higher corner frequency (passes the low and mid frequencies, but the low frequencies were cut by the high-pass filter, leaving you with the mid-band frequencies).

You can also perform band-pass filtering using the Equalization effect (http://manual.audacityteam.org/o/man/equalization.html). Note that the AM filter illustrated is a band-pass filter.

I don't know what audience this software is aimed at, but Iwith out bandpass filters, I can tell you who it's NOT aimed at. And that's science/electronics hobbyists.

Audacity is primarily a multi-track audio editor, so the primary audience is people producing, editing or processing audio. However, Audacity is extremely versatile and is widely used for many other purposes, including scientific use.

Now onto the second suggestion. FFT Filter.
This would allow you to add create your own custom filter based on FFT technique.

the Equalization effect is an FFT filter.

my suggested FFT Filter for Audacity would actually give you an option to set the frequency axis to either logarithmic or linear,

See the documentation (http://manual.audacityteam.org/o/man/equalization.html) It already has that.

and would also give you an option to set the amplitude scale to either dB (logarithmic) or mV (linear).

mV would be wrong unless you have a calibrated system. The waveform is just a series of numbers (samples). There is no "voltage" involved until it is converted back into an analog signal, and the voltage then depends on the electronic circuitry. if you have a signal that is +1 peak to peak, then the voltage coming out from your sound card will depend on the volume settings.
Linear scale would be a possibility, but as a close approximation, -6dB is a halving of the linear level, thus a peak level of -6 dB = 0.5 linear, -12 dB = 0.25 linear, -18 dB = 0.125 linear, and so on.

[Videogamer555]

A notch filter is a particular type of band-stop filter in which the stop band is very narrow.
http://en.wikipedia.org/wiki/Band-stop_filter

the makers of Audacity decided to leave out the bandpass filter.

You can perform band-pass filtering by applying a high-pass filter with a low corner frequency (passes the mid and high frequencies), followed by a low-pass filter with a higher corner frequency (passes the low and mid frequencies, but the low frequencies were cut by the high-pass filter, leaving you with the mid-band frequencies).

You can also perform band-pass filtering using the Equalization effect (http://manual.audacityteam.org/o/man/equalization.html). Note that the AM filter illustrated is a band-pass filter.

I don't know what audience this software is aimed at, but Iwith out bandpass filters, I can tell you who it's NOT aimed at. And that's science/electronics hobbyists.

Audacity is primarily a multi-track audio editor, so the primary audience is people producing, editing or processing audio. However, Audacity is extremely versatile and is widely used for many other purposes, including scientific use.

Now onto the second suggestion. FFT Filter.
This would allow you to add create your own custom filter based on FFT technique.

the Equalization effect is an FFT filter.

my suggested FFT Filter for Audacity would actually give you an option to set the frequency axis to either logarithmic or linear,

See the documentation (http://manual.audacityteam.org/o/man/equalization.html) It already has that.

and would also give you an option to set the amplitude scale to either dB (logarithmic) or mV (linear).

mV would be wrong unless you have a calibrated system. The waveform is just a series of numbers (samples). There is no "voltage" involved until it is converted back into an analog signal, and the voltage then depends on the electronic circuitry. if you have a signal that is +1 peak to peak, then the voltage coming out from your sound card will depend on the volume settings.
Linear scale would be a possibility, but as a close approximation, -6dB is a halving of the linear level, thus a peak level of -6 dB = 0.5 linear, -12 dB = 0.25 linear, -18 dB = 0.125 linear, and so on.

Ok, maybe mV is not correct then. But it SHOULD have an option for linear amplitude scale. PLEASE add that feature. That would be SO AWESOME.

And as for bandpass, there should be a bandpass filter. I shouldn't have to simulate a bandpass filter by using a highpass and lowpass filter, nor should I have to draw one out on the equalizer (which is great for more complicated shaped filters, but for simple bandpass it shouldn't be required). There SHOULD be a bandpass filter as a standalone filter.

And the Equalizer function should also have an FFT spectrum displayed in the background. It should (like Goldwave) have a slider that lets you select what time (the time of the first sample used) of the recording is being used to generate the currently displayed FFT spectrum in the display.

[steve]

I shouldn't have to simulate a bandpass filter by using a highpass and lowpass filter

It's not a "simulation". Applying high-pass and low-pass filters in series IS a band-pass filter.

You may also be interested in this plugin: http://forum.audacityteam.org/viewtopic ... 07#p204507

And the Equalizer function should also have an FFT spectrum displayed in the background.

The pale green line in the "Draw" mode shows the FFT response.
There is also "Plot Spectrum" which may be open at the same time as the Equalization effect (http://manual.audacityteam.org/o/man/plot_spectrum.html)
There are also the track Spectrogram and Spectrogram (log f) views: http://manual.audacityteam.org/o/man/tr ... tml#spgram

[Videogamer555]

I shouldn't have to simulate a bandpass filter by using a highpass and lowpass filter

It's not a "simulation". Applying high-pass and low-pass filters in series IS a band-pass filter.

You may also be interested in this plugin: http://forum.audacityteam.org/viewtopic ... 07#p204507

And the Equalizer function should also have an FFT spectrum displayed in the background.

The pale green line in the "Draw" mode shows the FFT response.
There is also "Plot Spectrum" which may be open at the same time as the Equalization effect (http://manual.audacityteam.org/o/man/plot_spectrum.html)
There are also the track Spectrogram and Spectrogram (log f) views: http://manual.audacityteam.org/o/man/tr ... tml#spgram

There should be a "plot spectrum" in the Equalizer dialog box, so that If I want to create a filter, based on the content of the spectrum display, I could do so (for example, cutting out unwanted signals at known frequencies, like the first 10 harmonics of 60hz hum, but not above that, because 60hz electrical harmonics are weak above that, and desired signal may be present above that). If I want to see exactly what the FFT content is, so I can draw a filter based on it, I will need to be able to display the FFT graph in the background of the equalizer window.

Also, I would prefer bandpass being available as a standalone filter, rather than needing to perform 2 steps (lowpass + highpass) EVERY SINGLE TIME that I want to use a bandpass filter.

[kozikowski]

You can save a filter for use later. You don't have to do it manually every time. If they're all different, then yes, that's a problem.

my hobby is related to science, not music

Audacity can be something of a science minefield. It's not a wave editor. It's a musical performance editor and some liberties are taken to make a show come out pleasing at the expensive of scientific accuracy.

For one serious shortcoming, the input signal and the output signal are different, nearly always. Audacity converts a performance Import into its own very high quality internal sound format and then, when you're done, converts it to your Export format. Even if you do little or nothing to it, the two ends of the process will easily be different. We get complaints that the wave data doesn't exactly match. Yes, but the guitar sounds grand, doesn't it?

Koz

[Videogamer555]

For one serious shortcoming, the input signal and the output signal are different, nearly always. Audacity converts a performance Import into its own very high quality internal sound format and then, when you're done, converts it to your Export format. Even if you do little or nothing to it, the two ends of the process will easily be different. We get complaints that the wave data doesn't exactly match. Yes, but the guitar sounds grand, doesn't it?

I'm not sure, but I believe if the input and output formats match exactly, the output should be the same. If the input is mono 16bits at 48000smp/sec raw PCM Wav file, and the output is also mono 16bits, at 48000smp/sec raw PCM Wav files, I believe they will match (except possibly for the header, if the output uses WAVEFORMATEX but the input uses PCMWAVEFORMAT)

[steve]

I'm not sure, but I believe if the input and output formats match exactly, the output should be the same.

Audacity does not "open" audio files, it "copies the data" from audio files when they are "Imported". By default Audacity will copy uncompressed audio data in "32 bit float PCM" format (irrespective of the original uncompressed format). It does this so as to provide the highest quality processing and avoid unnecessary / undesirable clipping at 0 dB. So when a 16 bit file is imported and then re-exported, the exported file is not (by default) exactly the same as the original 16 bit file, because it has been converted from 16 bit to 32 bit float and back down to 16 bit. In order for the conversion from 32 bit float to 16 bit to be exact, all of the 32 bit sample values must have exact representation as 16 bit integers, and "dither" must be turned off.

[Gale Andrews]

I shouldn't have to simulate a bandpass filter by using a highpass and lowpass filter

It's not a "simulation". Applying high-pass and low-pass filters in series IS a band-pass filter.

You may also be interested in this plugin: http://forum.audacityteam.org/viewtopic ... 07#p204507

And the Equalizer function should also have an FFT spectrum displayed in the background.

The pale green line in the "Draw" mode shows the FFT response.
There is also "Plot Spectrum" which may be open at the same time as the Equalization effect (http://manual.audacityteam.org/o/man/plot_spectrum.html)
There are also the track Spectrogram and Spectrogram (log f) views: http://manual.audacityteam.org/o/man/tr ... tml#spgram

There should be a "plot spectrum" in the Equalizer dialog box, so that If I want to create a filter, based on the content of the spectrum display, I could do so (for example, cutting out unwanted signals at known frequencies, like the first 10 harmonics of 60hz hum, but not above that, because 60hz electrical harmonics are weak above that, and desired signal may be present above that). If I want to see exactly what the FFT content is, so I can draw a filter based on it, I will need to be able to display the FFT graph in the background of the equalizer window.

It's a reasonable request IMO (but there are alternatives - 2.1.0 will let you draw a spectral selection and filter that selection using some Spectral Edit effects).

Audacity Wiki Feature Requests has ''Incorporate mini-spectrum plot (5 votes)" so I added your vote.

I would prefer bandpass being available as a standalone filter, rather than needing to perform 2 steps (lowpass + highpass) EVERY SINGLE TIME that I want to use a bandpass filter.

Perfectly reasonable IMO to argue that bandpass should be shipped and not just a Nyquist plugin. Nyquist plugins currently can't save their settings post session. I added your vote.


Gale

[steve]

Nyquist plugins currently can't save their settings post session

They probably can now, but there aren't any Nyquist plugins yet that do.