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SpecLab Waterfall Scene Capture Tutorial


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EDIT - I apparently cannot spell 'Tutorial'....mods, can someone change it?

Hey guys,

It is about time I got this thing up and running.

First of all you will need the following:

1. Latest Version of SpecLab:


Download it here: http://www.qsl.net/dl4yhf/spectra1.html#download

2. You will need Soho54's Audio Test DVD until I can get mine running:


Download it by clicking on the 2nd link in the first post. It is a self-extracting .rar of the .iso file.

3. The SCENECAP setting file (attached below).


1. Download SpecLab & install it.

2. Download the SCENECAP file below and open it in Notepad. Change the name using the 'Save As..' function to SCENECAPTURE.usr or SCENECAP.ini and save it to the 'configurations' folder wherever you installed SpecLab (usually C:\Spectrum).

3. Open SpecLab.

4. Use File->Load Settings From.. and choose SCENECAP as your configuration.

You should see something like this (please see the After Loading Config file below):

Now you are ready to finish up by:

1. Setting up your soundcard.

2. Calibrating level With soho54's Audio Test DVD

3. Correcting for any rolloff in the signal chain (soundcard, AVR, BD player)

Those topics will be addressed in the following posts.




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Setting up your soundcard and signal chain:



After loading the configuration file,  Go to:


Options->Audio Settings, I/O Device Selection


See the attached file below for the Dialog box that should pull up, then:


1. Choose Your soundcard from the Audio Input Device dropdown on the left.


2. Set your soundcard bits/sample to 16 or 24 depending on your soundcard's capabilities, on the lower left of the dialog box.


3.  Set your sampling rate to 44.1kHz or 48kHz depending on your soundcard's capabilities.  If you have a soundcard capable of more, just use 24 bit, 48kHz.




Now, set up your signal chain.  You will need to ensure that all the LF from all screen channels + LFE is going into your soundcard input.


You can do this by getting the feed directly from your BluRay player (if it decodes audio and does bass management for you), or you can get the feed from your AVR's Subwoofer Out.  If you get the feed from your AVR, you will need to do the following:


1. Disable any equalization or room correction (Audyssey, MCCAC, YPAO, whatever).

2. Set all speakers to 'SMALL' and set the crossovers to the subwoofer as high as possible (usually 200 or 250Hz).

3. Set all speaker distances to zero.

4. Set all speaker volume trims to -10dB to ensure headroom, and so your soundcard won't easily clip with high level content.



You will now need Soho54's Audio Test DVD.  Download and burn it if you have not done so already.





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Calibrating for Reference Level:


Play Soho54's Audio Test DVD.


1. Go to '5.1 DD Tests'


2. Go to 'Manual Tones'


3. Go to 'LFE'


I assume you have SpecLab up and running, and have set up your AVR or BluRay to send a bass-managed signal to your soundcard.  You will now use the Spectrum Graph Area at the top of the screen.


4. Play the 60Hz tone.  It is encoded at -20dBFS, which means that through a properly calibrated AVR, it will have a level of 95dB on an SPL meter.  


5. You should see something like the screen attached below (60Hz Calibration) for the duration of the tone.


You will now adjust the volume on your AVR so that the 60Hz tone will be right around the -30dB line (see attached pic).


6. Go back to the 5.1 DD Tests page.


7. Go to 'Extras' 


8. Go to '-0.5dB LFE'


9. Play the 20Hz tone.


The tone should just touch the -10dB line.  See the attached pic.  In the attached pic, you can see three things:


   A. The tone is at -10dB on the upper scale.

   B. There was a 'pop'  a few seconds after the tone began, that is my WiFi card....I turn it off when I am running PvA.

   C. There is some 3rd HD and 5th HD in the trace.  I am not clipping my soundcard input, nor my receiver out (verified independently), but the soft clip is at the bluray player, or encoded on the disc, I'm not sure which.  It is still a good way to calibrate.



Why -10dB?  Because the worst case scenario for a 5.1 track is if every single channel has 0dBFS LF material encoded in it, you end up getting 125dB.  This ensures your soundcard will just start to clip if the worst case scenario actually happens.


You are now almost ready to capture scenes.  WRITE DOWN your Soundcard Input and AVR volume settings, so that you can have apples/apples comparisons.  Always set them the same, and re-calibrate every now and then with the Soho DVD.



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Correcting for Roll-Off in the signal chain:


1. I am assuming you have done EVERYTHING above.


2. By now the red and green lines in the upper graph are driving you nuts.  You can turn them on and off by Going to:


   A. Options -> Spectrum Display Settings

   B. In the middle of the new dialog box, there are two checkboxes.  One is Peak Holding graph, and the other is Long term Average.

   C. To clear the Peak graph, uncheck the box, click the 'Apply' button, and recheck the box and 'Apply' again.  

   D. To clear the Average line, hit the 'clr' button to reset the Average, or uncheck and click 'Apply'.


3. Reset the peak graph using C above.


4. Set your AVR volume 10dB above your setting in the previous post.


5. Fire up Soho54's DVD.


6. Go to the -.5dB LFE page, and start with 1Hz, and the DVD will play every single tone, including all the LFE sweeps.  they should just hit the 0dB line on the upper graph, and should nearly if not clip your soundcard.


Here's what you end up with (see attached):


You can see my input is clipped on the right side waveform (as it should be), and the harmonics are visible on the waterfall.  It does not start out clipped because my subwoofer lowpass is set at 250Hz, so it start rolling off prior to that.


You can also see the rolloff of the green peak trace.  Here is how to correct for it:


1. In SpecLab, go to 'Options' then 'Reference Spectrum'

2. In the dialog box, click the 'Copy from Peak Holding Graph' button.

3. In the dialog box, click the 'Save Reference as file' button and save.  I use 'Rolloff Cal' as my filename.

4. In the dialog box, check 'subtract (for display only)' button.

5. Click 'Apply'.


Now, let's double check to make sure the calibration worked:


1. Turn your AVR down to the original setting you used to calibrate (10dB lower than above).

2. Play one of the tones in the Soho -0.5dBLFE section that would have been rolled off.

3. If you did everything right, the tone should just touch the -10dB mark, like attached (3Hz tone, the bar just touches -10dB).


You can see that even though the color bars and spectrum are now calibrated, as well as the average red trace, the peak green trace will rolloff as before.  This form of roll-off correction is only good for scene captures, I have to correct the PvA graphs another way.


After doing this, Go to 'File' -> 'Save Settings As' and save your settings so that your rolloff calibration will always be included automatically.


You are now ready to graph some scenes!!!



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Getting a scene capture:


1. Set up everything as above.


2. Queue up a fav scene - In this case, The Incredible Hulk Sonic Cannon scene, and allow it to play while SpecLab is running.


3. As the scene is finished, click 'Capture Now' on the left side of the screen.  Look in your SpecLab folder, and you should see a file called capt********* in the folder, or in the 'screenshots' folder, a file called Capture**.  Rename it so you know what it is, and post it up to the forum!


You can add timestamps and sceneshots if you have the capability (like Bosso does).  I do not.


Here's the scene (attached with comments):


If you want to get rid of the upper graph after calibration, go to:


   1. Options -> Spectrum Display Settings -> 

   2. In the top right of the dialog box, there is a Show: with a pulldown.  click on it and select 'Waterfall Only' and Apply.

   3. No more graph on top.







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PvA will take a lot more time to explain to correct for the rolloff, it took me many tries to get it right....


If you think that the above graphs are too coarse, it's because it is the same settings I use for PvA, which is a compromise between resolution and rise-time.  It is easy to change.



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  • 2 weeks later...

The 'http://jarrodchristman' link will automatically start the download of the .iso, that you can then burn to DVD-5 with imgburn (free).


You should not need the mic or preamp for scenecaps. We try to get what is on the disc with a scenecap. People that have flat response to 3Hz can use a mic, but for true apples/apples, using the method above is pretty good....




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Got the link working now and I have downloaded the file and burnt it to a DVD. Those next steps look a bit intimidating. 


One question, if I was going to go straight from an Oppo BDP-95, what kind of cabbling would I need? I cant go from my reciever as it is not a conventional one. 


Cheers Dave

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Yes, you can do it by having the BDP95 do the bass management for you, it's on page 70-73 of the manual.  Set all the speakers to 'small', and change the crossover frequency for all the satellites to 250Hz, as well as the lowpass for the LFE (if you can).  You are then set and can use the variable output level to set reference on your soundcard as above.  



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  • 7 months later...

OK, so I had a practice run with 'The Croods', I sent the entire film through as a mono WAV file following the instructions on AVS.


Does the attached image look correct? 


Also what does the -20db etc mean in real world listening volume? 95db?


Many thanks


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Not that I am aware of. I view the 'whole film' wav in Audacity or WaveShop and find the best bits (both programs have a spectral graph), then save each scene as their own wav files to graph as individual scenes with SpecLab. I add 30 sec of silence before and after short clips so SpecLab won't have a problem with it.



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