Audacity Forum

steve wrote:

Gale Andrews wrote:What was the developer's rationale?

basically that it is as good a way as any for plotting the spectrum of multiple channels. There are pros and cons to any method.

Would you support an option to average multiple tracks/channels?


Gale

Gale Andrews wrote:Would you support an option to average multiple tracks/channels?

I don't see that has any great benefits over other methods. If you have two identical audio channels, would you not expect the amplitude for each frequency bin to be 6dB higher than just one audio channel?

If we decide that we want to provide options, then really would should provide many options, not just an arbitrary two of many.
What exactly do you mean by "average the multiple tracks"? Do you mean that you mix the channels, then divide by the number of channels, then plot the spectrum of that, or do you mean that the plot should be the average of analyzing the channels independently?

I would support "per channel" graphs. (a different coloured line graph for each channel).

I think the most pressing need for Plot Spectrum is to be able to manually scale the graph rather than the forced auto-scaling.

steve wrote:...
I would support "per channel" graphs. (a different coloured line graph for each channel).
I think the most pressing need for Plot Spectrum is to be able to manually scale the graph rather than the forced auto-scaling.

+1 and +1

-- Bill

steve wrote:

Gale Andrews wrote:Would you support an option to average multiple tracks/channels?

I don't see that has any great benefits over other methods. If you have two identical audio channels, would you not expect the amplitude for each frequency bin to be 6dB higher than just one audio channel?

It's not obvious to everyone where you have a stereo pair. Even you questioned it once.

steve wrote:What exactly do you mean by "average the multiple tracks"? Do you mean that you mix the channels, then divide by the number of channels, then plot the spectrum of that, or do you mean that the plot should be the average of analyzing the channels independently?

Both could be useful, though they are somewhat fringe options for mono tracks. The confusion is with stereo tracks where the peak in the spectrum analysis is higher than the peak when you play or export.

steve wrote: I would support "per channel" graphs. (a different coloured line graph for each channel).

That would currently still show +6 dB for each channel of a stereo pair in the case in question, wouldn't it?

Gale

Gale Andrews wrote:Both could be useful, though they are somewhat fringe options for mono tracks.

In that case I don't know what you mean by "average multiple tracks/channels".

Gale Andrews wrote:The confusion is with stereo tracks where the peak in the spectrum analysis is higher than the peak when you play or export.

The peak in the spectrum may be higher than the peak when you play or export. If the signals are out of phase the sum (and the average) will be lower.
The difference being that the peak when you play or export is "per channel" whereas Plot Spectrum is not.

Gale Andrews wrote:

steve wrote:I would support "per channel" graphs. (a different coloured line graph for each channel).

That would currently still show +6 dB for each channel of a stereo pair in the case in question, wouldn't it?

No, it would show one line for the left channel and one line for the right channel - traditionally the default colours would be blue and red respectively. The blue line would show the same values as if you had analysed only the left channel and the red line would show the same values as if you had analysed only the right channel.

Usually such spectrum plots allow you to temporarily save a graph and plot another on the same screen in another colour, thus allowing easy comparison between spectra.
Here's an example:

steve wrote:

Gale Andrews wrote:

steve wrote:I would support "per channel" graphs. (a different coloured line graph for each channel).

That would currently still show +6 dB for each channel of a stereo pair in the case in question, wouldn't it?

No, it would show one line for the left channel and one line for the right channel - traditionally the default colours would be blue and red respectively. The blue line would show the same values as if you had analysed only the left channel and the red line would show the same values as if you had analysed only the right channel.

OK so that would solve the possible confusion when dealing with a stereo pair so I'll vote for that too.

Would we not want a checkbox to turn per channel display on and off?

steve wrote:Usually such spectrum plots allow you to temporarily save a graph and plot another on the same screen in another colour, thus allowing easy comparison between spectra.

+1.

Also I moved this to "Adding Features" but I already counted the votes as I went along.


Gale

Gale Andrews wrote:Would we not want a checkbox to turn per channel display on and off?

I think the default behaviour should be to show one trace per selected channel.
Although it is not very friendly for colour-blind users, I think this is the only unambiguous way to present data from multiple channels

Optionally, yes we could provide one or more options for combining multichannel plots.

There are a lot of ways that we could do that. Here are some random ideas:

• Checkbox: Stereo tracks mixed to mono.
• Checkbox: Mix of all selected channels (as now).
• Checkbox: Normalised mix of all selected channels (0 dB in the same frequency band in all channels with identical phase shows as 0 dB).
• Checkbox: Average left/right plots of stereo channels.
• Checkbox: Difference between left/right plots of stereo channels.
• Group plots: Select two or more plots and enable them in a "group".
  The "group" can be set to show:
  • Individual plots for each spectrum in the group (default)
  • the maximum for each spectrum in the group
  • the minimum for each spectrum in the group
  • the average for each spectrum in the group
  • the spectrum for a mix of all channels in the group (requires that the channel exists)
• Other....

steve wrote:

Gale Andrews wrote:Would we not want a checkbox to turn per channel display on and off?

I think the default behaviour should be to show one trace per selected channel.

So I'm clear, does that also mean per selected track, so with 6 selected tracks there are by default six traces? Or only for stereo pairs and tracks assigned to Left or Right?

An obvious issue is handling of multi-channel files, which import as all mono tracks or first two left and right and the rest mono, according to the importer.

steve wrote:Although it is not very friendly for colour-blind users, I think this is the only unambiguous way to present data from multiple channels

Could there be a High-Contrast View? Perhaps it would have to number the traces at various points and give the key underneath as to which track each number referred to?

Do you have any favourites in your long list of options?


Gale

Gale Andrews wrote:So I'm clear, does that also mean per selected track, so with 6 selected tracks there are by default six traces? Or only for stereo pairs and tracks assigned to Left or Right?

One trace per channel.
If you select one stereo track and 2 mono tracks, Plot Spectrum will show 4 traces.

Gale Andrews wrote:An obvious issue is handling of multi-channel files, which import as all mono tracks or first two left and right and the rest mono, according to the importer.

It could be very convenient fro identifying the LFE channel.

Gale Andrews wrote:Could there be a High-Contrast View? Perhaps it would have to number the traces at various points and give the key underneath as to which track each number referred to?

If I can have a wish without having to program it myself
I would have a status bar message (or similar) when the mouse pointer is directly over a trace, indicating the track number, track name, and for multichannel (stereo) tracks - the track channel. For example: "Track 1 - Audio Track - Left channel".

Gale Andrews wrote:Do you have any favourites in your long list of options?

Not yet
I'd start with getting the per-channel plots working, then try out some options as experimental features and gather user feedback.

The ability to compare spectra is a very useful feature, but the current Plot Spectrum is very poor for doing so. Addressing that shortfall would be high on my agenda for improving Plot Spectrum.

steve wrote:

Gale Andrews wrote:So I'm clear, does that also mean per selected track, so with 6 selected tracks there are by default six traces? Or only for stereo pairs and tracks assigned to Left or Right?

One trace per channel.
If you select one stereo track and 3 mono tracks, Plot Spectrum will show 4 traces.

I'm still unclear. I understood you to say that for a stereo track, it would show one line for the left channel and one line for the right channel (both at about 0 dB for a 440 Hz sine)? That would make five traces for a stereo track and three mono tracks.


Gale