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PostPosted: Mon Sep 14, 2009 1:04 pm 
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In most of the SBU stereo-to-surround methods a gain panel is present which allows for controlling the individual gain levels (positive or negative) for each of the 5.1 channels. This guide will explain the usage of a spreadsheet tool that will facilitate the calculation of these individual gain levels based on user input criteria.

The spreadsheet (v4.5) can be found here below
Attachment:
Gain_Group_In_Bidule_Aid_v4.5.rar

This guide will contain the following sections:

Enabling Macros in Excel
Before using the spreadsheet, ensure that the security settings in Excel are such that a macro can be executed.

In Excel 2003, go to Tools/Options and choose the Security tab. Deselect the “privacy options”, click on the “Macro Security” button and put the level at Medium. Save the spreadsheet with these new options. Close the spreadsheet, and open it again. In the dialog window that will then be opened, select the “Enable Macros” option.

In Excel 2007, click the Office Button (top left) and go to Excel Options. Select Trust Center/Trust Center Settings. Go to Macro Settings and choose “Disable all macros with notification” (this could already be selected by default).


Go to Privacy Options and deselect the “Remove personal information...” option.


Save the spreadsheet, close it and re-open it again in Excel. In the Security Warning that is displayed on the top, choose Options and select the “Enable this content” option.
For info, the macro functionality is needed to enable the “Clear Values” button (see later). No other macros are present in the spreadsheet.

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Spreadsheet Input
Let’s work with an example to clarify the functionality of the spreadsheet.
Suppose that after a first run of an SBU plogue bidule for a certain input file, the output monitors (RMS buddies) give for each of the channel pairs, Front-left/Front-right, Center/LFE and Surround-left/Surround-right, the following results for the average RMS (loudness) and absolute peaks. For more information on RMS see http://en.wikipedia.org/wiki/Root_mean_square.


Important: The absolute peak of all channels must all show a negative value. If there is somewhere a positive (+) value in the absolute peak, then that means that there could be clipping and the bidule should be rerun by lowering the pre-processing master gain sufficiently to resolve the clipping, prior to using the spreadsheet.

Open the spreadsheet. Optionally, click the “Clear Values” button (see 1.) to clear the spreadsheet of unnecessary values entered previously. The spreadsheet can be cleared manually, but there is a high risk that a formula gets erased by accident, so it is better to use the button for that purpose.
Enter in one of the Track lines of the spreadsheet the Average RMS and Absolute Peak values for each of the corresponding channels without the minus sign (see 2.).

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Spreadsheet Calculation Parameters
Depending on the user input criteria, the spreadsheet will calculate the individual maximum gain levels for each of the channels avoiding any possible clipping (see 4.).
In the example here below, taking into account the input criteria, the maximum to which the Front channels can be (in this case) increased is to an average RMS of -19dB and so forth for the other channels (see later). This calculated maximum for the Front channels will always be an integer value.


The possible user input criteria are
  • The amount of dB the Rear surround channels should be lower than the Front channels (see 1.). Since the surround speakers are normally closer to the listening position than the front speakers, a value of 3dB is a good starting point. This value ranges normally between 0 and 3dB, depending on the SBU stereo-to-surround method.
  • The amount of dB the Center channel should be higher than the Front channels (see 1.). This value ranges normally between 0 and 2dB, depending on the SBU method.
  • Whether or not a gain should be calculated for an additional LFE channel produced by the SBU method (normally enabled through a “bass boost” option inside the method). In the spreadsheet, choose “Yes” for “Bass Boost?” and an absolute peak value for the LFE channel (see 2.). The value ranges normally between a -10dB to -4db peak value.
  • A safety margin (see 3.) to be used in all calculations. For example, putting 1dB in the example here below will lower the average RMS level of all channels with 1dB, decreasing therefore the Front channels from -19dB to -20db. By default leave the safety margin at 0dB.

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Spreadsheet Result


The gain values (including the sign, if present) can now be entered in the gain panel of the SBU method, as shown here below.


A re-run of the SBU method with these gain values will show the following result in the Output monitors.


Notice that the Front channels are both on average at an RMS of -19db (see 1.) and that the Surround channels are 3dB lower, at -22dB (see 2.). Moreover, the Center channel is 0.5dB higher than the Fronts, at -18.5dB (see 3.), and the peak of the LFE channel is capped at -4dB (see 4.).

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Normalisation
The spreadsheet has the possibility to normalise the calculated average RMS values of the Front channels between all Tracks based on the average RMS of the original input files.
As shown here below, take for example that a second Track is added with its Average RMS and Absolute Peak values for each of the channels.
Moreover the average RMS, without the sign, of the left and right channel of the original input files for Tracks 1 & 2 has been entered in the columns OL and OR (Original Left and Original Right). These values can be obtained from an additional monitor (RMS buddy) fed by the original input file. If this monitor is not present, it can be easily added as explained in the Plogue Bidule - Basic Guide, section 7.


The spreadsheet has calculated that the original input files have an average RMS value of -16.6dB and -15.3dB, for Track 1 and 2, respectively (see 1.). This means that Track 2 sounds 1.3dB louder than Track 1. This absolute difference between both Tracks will now be used in the calculation process (see further).


Notice that the calculations in the spreadsheet have now forced the average RMS of the Front channels of Track 2 to change from -17.0dB to -17.7dB (see 2.).
This is explained by the fact that the calculated average RMS of the Front channels of Track 1 is at -19dB, and since Track 2 should be 1.3dB louder than Track 1, this results in a (-19dB + 1.3dB) = -17.7dB for Track 2. Without normalisation, Track 2 would have been 2dB louder, i.e. -17dB versus -19dB for Track 1.
All tracks that are normalised will show a red “Normalised ==>” line. For these normalised tracks, enter in the gain panel the values shown in red. The loudest track (Track 1 in the example above), towards which all other tracks are normalised, does not have such a red line. For this track, enter in the gain panel the values shown in black.

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History
2009-09-14 : Initial Version published in Wiki (Pl4yitLOUD)

This guide is Copyrighted © 2009-2010, SurroundByUs.com


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