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--- en:wiki:anhang:anleitungen:the_repeated_stereo_pairs_method [27/09/2016 19:38] – created matt
+++ en:wiki:anhang:anleitungen:the_repeated_stereo_pairs_method [28/09/2016 19:39] (current) – [Step 2: Gain Management and the LFE Channel] matt
@@ Line 5: / Line 5: @@
 The following factors may be relevant for a complete correction but are out of scope of this document;
-- any basic room correction issues (what crossover to use, macro parameters, use of prefilters etc)
+  * any basic room correction issues (what crossover to use, macro parameters, use of prefilters etc)
-- subwoofer time alignment
+  * subwoofer time alignment
-- multisub configuration
+  * multisub configuration
-- multiway main channels
+  * multiway main channels
-- driver linearisation
+  * driver linearisation
 The example provided is for a 5.1 system using JRiver for playback.
@@ Line 25: / Line 25: @@
 Use the mic alignment tool and measure offsets between the reference channel and each other channel. For example, if you use L as the reference channel then you need to know the delay (in samples) for
-L-R
+  * L-R
-L-C
+  * L-C
-L-SL
+  * L-SL
-L-SR
+  * L-SR
 Record these delays. I recommend recording them permanently and returning the mic to the same position for future measurement sessions.
@@ Line 43: / Line 43: @@
 For each of LC, LSL, LSR
-- either manually initialise the workspace as above OR copy the entire LR directory and do a search and replace in the acourate.ini to replace the folder name (using scripting language of choice)
-- apply delay adjustment to XO2R to account for delays found using mic alignment tool
+  * either manually initialise the workspace as above OR copy the entire LR directory and do a search and replace in the acourate.ini to replace the folder name (using scripting language of choice)
+  * apply delay adjustment to XO2R to account for delays found using mic alignment tool
+=== unix (cygwin) script to copy workspaces ===
+An example which copies LR to the 3 fresh workspaces above, run from the parent directory
+<code bash>
+for target in LC LSL LSR
+do
+    mkdir ${target}
+    cp LR/XO*.dbl ${target}/
+    cp LR/Target.dbl ${target}/
+    sed -e "s/\\\LR/\\\\${target}/g;s/\\\LR\\\/\\\\${target}\\\/g" LR/Acourate.ini > ${target}/Acourate.ini
+done
+</code>
+If using shared prefilters (e.g. for manual IIR on the subwoofer) then place these in a separate common directory.
 ===== Measurements =====
@@ Line 64: / Line 80: @@
 For each of LC, LSL, LSR
-- open the workspace
+  * open the workspace
-- configure the signal chain to route channels accordingly
+  * configure the signal chain to route channels accordingly
-- do a quick log sweep
+  * do a quick log sweep
-- run macro 1
+  * run macro 1
-- load the "reference" target curve into slot 3
+  * load the "reference" target curve into slot 3
-- if a negative gain adjustment is required, apply the negative gain adjustment and save as a dbl overwriting your "reference" target curve
+  * if a negative gain adjustment is required, apply the negative gain adjustment and save as a dbl overwriting your "reference" target curve
 Copy the "reference" target curve file into every workspace
@@ Line 77: / Line 93: @@
 For each of LR, LC, LSL, LSR
-Open the workspace
+  * Open the workspace
-Run a log sweep
+  * Run a log sweep
-Run macro 1
+  * Run macro 1
-Run macro 3
+  * Run macro 3
-Compare inverse curves against pulses, run "phase extract" to avoid unnecessary boost at extremities and save phase extracted pulses over the Pulse48Linv/Pulse48Rinv as necessary
+  * Compare inverse curves against pulses, run "phase extract" to avoid unnecessary boost at extremities and save phase extracted pulses over the Pulse48Linv/Pulse48Rinv as necessary
-Iterate over macro 4 & macro 5 until an acceptable result is achieved
+  * Iterate over macro 4 & macro 5 until an acceptable result is achieved (NB: it is advisable to use the same parameters on the reference L channel in every workspace)
-(NB: it is advisable to use the same parameters on the reference L channel in every workspace)
 If there is a non zero delay between XO2L and XO2R (i.e. the mic alignment tool did not report 0 offset)
-- Load Cor1L and Cor1R, find the peaks, calculate peakoffset = Cor1L-Cor1R
-- Rotate Cor1R by (Cor1L-Cor1R) samples, save over Cor1R
+  * Load Cor1L and Cor1R, find the peaks, calculate peakoffset = Cor1L-Cor1R
-- Rotate Cor2R by (Cor1L-Cor1R) samples, save over Cor2R
+  * Rotate Cor1R by (Cor1L-Cor1R) samples, save over Cor1R
-- Remember to update the Cor wav files if using (e.g. Load Cor1L into slot 1, Cor1R into slot 2, save as stereo wav and overwrite Cor1S)
+  * Rotate Cor2R by (Cor1L-Cor1R) samples, save over Cor2R
-- Remember to repeat for all sample rates if generating filters for multiple sample rates
+  * Remember to update the Cor wav files if using (e.g. Load Cor1L into slot 1, Cor1R into slot 2, save as stereo wav and overwrite Cor1S)
+  * Remember to repeat for all sample rates if generating filters for multiple sample rates
+Special note for surround channels…. if you find that there is a markedly different correction applied to the surround channels then it may be better to compare SL to SR rather than SL to L and SR to L. Use your eyes and ears to judge this.
-Special note for surround channels.... if you find that there is a markedly different correction applied to the surround channels then it may be better to compare SL to SR rather than SL to L and SR to L. Use your eyes and ears to judge this.
 ==== Step 3: Correcting the LFE channel ====
@@ Line 173: / Line 190: @@
 ==== Step 2: Gain Management and the LFE Channel ====
-COMING SOON!
+This configuration is summing multiple input channels into one subwoofer output channel as well as applying a +10dB gain increase to the LFE input channel. If you simply use the convolver cfg above to do this, you will digitally clip the subwoofer channel during this process. This diagram illustrates the signal chain
+{{http://cdn.soundandvision.com/images/archivesart/805bass.4.jpg}}
+This means there needs to be some gain adjustments performed on each channel both before and after summation to avoid clipping. In particular note that the optimal implementation is likely to require an awareness of gain structure across your signal chain as it may leverage the input sensitivity and downstream amplifiers.
+One jriver centric implementation when using a 5.1 output format is;
+Making Room for Summation and Adjusting the LFE channel
+  * move a PEQ block above the convolver
+  * add an "adjust the volume" option, set gain to -15 and channels to "Left, Right, Centre, SL, SR"
+  * add an "adjust the volume" option, set gain to -5 and channels to "sub"
+Recovering Gain after Summation
+  * move a PEQ block below the convolver
+  * add an "adjust the volume" option, set gain to +15 and channels to "Left, Right, Centre, SL, SR"
+  * adjust downstream output gain/input sensitivity on the subwoofer signal chain to recover 15dB relative to the main channels
+Note that this implementation allows headroom of 5dB (in the LFE + low passes) before digital clipping will occur. A theoretical worst case signal will require about 3dB of additional attenuation (and subsequent recovery) to pass through cleanly. This sort of signal is exceedingly rare (non existent?) so it is a decision for the user as to how much headroom to leave.