Spectrum Views

We are currently looking for beta testers around the world to help test our forthcoming application Har-Bal 3.0
To apply to be a Har-Bal 3.0 beta tester all you need is to be a current/registered owner of Har-Bal and contact us with your request via email from our contact page.
Currently there is no manual provided. Registered users will have no problem navigating around the new version
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HarBal
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Spectrum Views

Post by HarBal »

This question regarding views came from one of our beta testers and I shall attempt to explain.

I have some other questions but the main one I'm interested in is the spectral views. (I'll ask about the dynamics later!)

If I see, for example, a mid spectral trace, and I'm creating a filter, it still affects the entire stereo file - at least that's what I ultimately heard. I did notice when I created a filter when the mid trace was displayed (and then view the filter shape via the ALT+2 display), it would change when I selected to view the side trace provided, of course, I edited a filter shape when the side trace was displayed.

I initially thought I was creating separate filters for mid and side components. But I noticed when I created a filter when the mid trace was displayed (and let both the original and filtered trace show), when I switched to the side trace, it would display adjustments even though I made no edits yet to the filter while displaying the side trace.

I hope this explanation is not confusing!

If I'm creating a single composite filter, why display only components (ie: mid, side, left, right) of the filter? I would need to see what I've done to the file as a whole.

I can understand having 5 views (adding a composite view to the list), and being able to filter left, right, mid, side components independently when needed.


Mid / Side decoding is defined by the following equations:

Mid = Left + Right
Side = Left - Right

You can see that with a mono source Side = 0 as Left = Right. So the level of the Side component relative the Mid component gives an indication of the stereo spread of your mix.

Now the basic Har-Bal 3 filter block has left and right channels being filtered by left and right filters, then being encoded into Mid and Side using the above scheme with Mid and Side filters applied to those components and then being decoded back into Left and Right.

To get back to Left and right we use the following equations:

Left = (Mid + Side) / 2
Right = (Mid - Side) / 2

Considering all that and your observation why (1)Har-Bal doesn't have a composite view and (2) why a change in the mid filter appears in the side filter I can now give a clear explanation.

The most common view to use in Har-Bal for EQ is the Mid view because to corresponds to the mono'ing of the source and therefore contains the entire spectrum content of the track (remember Mid = Left + Right which is mono). This is essentially equivalent to the filtering of Har-Bal 2.3 as far as what your see in the spectrum.

Now to answer why Side should change when you make an edit in mid you need to consider the second set of equations for reconstructing Left and Right from Mid and Side. You'll note that both Left and Right depend on both Mid and Side so if you were to apply a filter change to the mid component and not reflect it in the side component you WILL alter the stereo image. Given that the intention of the mid view in Har-Bal is the equivalent of what you call "composite" we don't want the stereo image to change so any edits in mid go into side.

The converse is not true however. If you wish to make a change in side it is assumed that you want to change the stereo image (that is the point of the separate side channel filter) so any edit you make there is only in that channel. The next question you might have is what effect does a change in Side have on the stereo image. Well, if you look at the "decoding to left and right" equations again you will see that Side is added to Mid to give Left and subtracted from Mid to give Right. So you should be able to see that as Side approaches zero the Left approaches the right or in other words, tends to mono. Now you can make side tend to zero by providing a filter cut. So, as a general rule, if you want to widen an image you provide side boost and if you want to narrow the image provide a cut. A simple example that is useful for mastering for vinyl is mono bass which you can create by applying a high pass shelving filter with knee around 300 Hz.

cheers,


Paavo.
janpetter
Posts: 45
Joined: Sat Feb 05, 2005 7:00 pm

Re: Spectrum Views

Post by janpetter »

I was wondering when you apply Har-Bal Air , would it not effect mid and side ?
It would be nice to see the changes it apply to the spectrum .

All the best
Jan
HarBal
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Posts: 761
Joined: Mon Apr 19, 2004 8:18 pm
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Re: Spectrum Views

Post by HarBal »

Predicting the effect that air has on the spectrum is computationally taxing and more effort that it is worth. That is why it isn't included, nor the effect of left / right filters on mid and side spectrums for the same reason.

The effect air has on the spectrum is actually rather small when used modestly. It is realised as a log normal random deviate applied to a unity gain all pass response with the variance of the deviate tapering at higher frequencies to add warmth. Without the taper it would sound to bright. How the air then affects spectrum then depends apon whether the peaks and troughs of the air response line up with the peaks in the spectrum. That alignment can't be accurately re-constructed with the analysis results because the spectrum resolution is reduced to 1/12th octave and the peaking and troughing of the deviate is finer scale than that. That is why it is not practical to calculate.

For that matter, the effect of dynamics processing is not accounted for in the average spectrums either, again because it would require a lot more computational effort with not a lot of benefit.

cheers,


Paavo.
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