Helpful ReplyQuestion about Pure Tone Testing

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meh
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2011/03/01 17:06:10 (permalink)

Question about Pure Tone Testing

So I have been trying to trace a distortion problem that I think I have involving some of the different plug-in's.
In the olden days we used to calibrate the audio chain using pure tones to set levels are to find bad connections and a host of other things.
I tried to set up the same kind of test in X1P using the Pentegon I as the pure tone source. 
I made a whole note and then  changed it's duration to 400 to give me a long test tone on a MIDI track.
I assigned it to an Audio track.
When I hit play the wierdist thing happens the inital volume according to the audio meter is about -12db and then after a few seconds it starts dropping to about -16db and then stablizes to that value.
 
Not sure why?
Is there a plugin meter that can be sued to get more accurate info?
 
Thanks In Advance
 

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    AT
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    Re:Question about Pure Tone Testing 2011/03/01 18:02:47 (permalink) ☄ Helpful
    Sound Forge (even the cheap version, I think) will create test tones.  I would think the envelope in the Pentegon is doing something, but I've never played with it enough to give advice.  Try an online search for pure test tones - I bet you can find something.

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    The Maillard Reaction
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    Re:Question about Pure Tone Testing 2011/03/01 18:09:19 (permalink) ☄ Helpful
    Do you ave a compressor in your signal chain?

    Every plug-in should have an input and output meter... but many don't.

    One infamous example is Pro Channel... all it has is a gain reduction meter... but that only works when you want it too.

    In any case, you simply have to follow the circuit, as you have begun too, and search out the over driven stage.

    There are a few free standing meter VSTs that you can find and place in between other plug ins if you can't find it just using your ears.

    Have fun!

    best regards,
    mike

     


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    drumr
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    Re:Question about Pure Tone Testing 2011/03/01 22:31:47 (permalink) ☄ Helpful
    http://homerecording.about.com/od/homestudiobasics/a/test_tones.htm
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    Jeff Evans
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    Re:Question about Pure Tone Testing 2011/03/01 23:26:10 (permalink) ☄ Helpful
    Firstly drumr has a good point. Test tones are a much better option than trying to get a synth to create a test tone. Now the website he has recommended has some test tones on there but you should be aware of the level of these tones.

    How do we express the level of a continuous tone. Well we use the term rms to express this but there can also be some confusion here. A standard is used that gives us the very tops of the sinewave peaks as the ref level. But in actual fact the rms level is 3 db down from that but for the purposes of this, think rms level is the very top of the sine wave.

    Now the test tones that drumr has suggested are right at the full monty of 0 db FS which is seriously loud. So you might need to consider that you would rarely if ever send any rms signal around at 0 db FS! Also these tones are short and you will need to extend them while you are trouble shooting.

    Now this is why I go on about K System levels. There are three K system levels of K-12, K-14 and K-20. I tend to use K -14 a lot for general work. So you might want to reduce the level of these tones say down by 14 db before you go feeding them into any plugins. The tones in their present form will blow every plugin away. Where as around -14 might be much more typical of an average rms or average level.

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    #5
    The Maillard Reaction
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    Re:Question about Pure Tone Testing 2011/03/02 07:36:12 (permalink) ☄ Helpful

    Jeff's trying to bestow confusion upon you.

    The tones from homerecording site are peaking at 0dBFS and so it is true that they are going to rather hot for testing. But their levels are easy to define. They are peaking at 0dBFS and can be said to have a RMS value of -3dBFS because the tones in question are sine waves and this description conforms to the definition specified in AES Standard AES17-1998.



    The K system spoken about above is a monitor calibration system. Here's what the person who named the K system after himself says about using the K- system:

    "Tracking/Mixing/Mastering
    The K-System will probably not be needed for multitracking--a simple peak meter is probably sufficient."

    That's from http://www.digido.com/lev...udes-the-k-system.html




    Another pair of quotes from that essay that I find interesting to consider simultaneously:


    "the VU meter is a very primitive loudness meter. In addition, current digital technology permits us to easily correct the non-linear scale, its dynamic range, ballistics,and frequency response."

    "When the K-System is not available
    Current-day analog mixing consoles equipped with VUs are far less of a problem than digital models with only peak meters."







    To summarize, you can make a nice looped sample tone at 1kHz anywhere from -18dBFS through -12dBFS and you may find it is very useful to run through your signal chain so that you may easily find a gain stage that is set too hot.

    I don't think you really need a test tone unless you are an engineer making actual measurements of amplitude change and distortion... you can probably use any source material on the track or bus.

    The pink noise mentioned in the digidoo link is a substitute for source material... but it sounds too uncomfortable to use by ear and it's unsuitable for many amplitude measurements and all distortion measurements.

    Source material like your favorite song will work very well as an all around "test tone"



    I suggest that the more important aspect of trouble shooting gain staging is developing familiarity with a diagnostic procedure for tracking down the culprit. Learn to isolate the problem by eliminating possibilities. It will get a lot easier when you learn where the gain stages that are not metered are hiding.


    all the best,
    mike


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    meh
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    Re:Question about Pure Tone Testing 2011/03/02 08:01:45 (permalink)
    Thanks Mike;
    It is the troubleshooting aspect that most intrests me.  I just thought that there needs to be a baseline or reference which is why I was using pure tones. 
    Since I started down this path I have learned alot about the signal-chain through X1P but to quote jl the more I learn the less I know.  But the good news is so far the Physics does not lie.
    Thanks to all for the info here...
     

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    The Maillard Reaction
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    Re:Question about Pure Tone Testing 2011/03/02 08:38:58 (permalink)

    I use 1kHz tones in my TV work all the time... but it seems like no one listens to it.

    For example on a live TV satelite shot I may have tone up for 30 minutes prior to going live... and then 15 seconds from air when I bring the mics up some mix engineer 2000 miles away shouts into my earpiece "It's too loud" or "It's not loud enough" and I shout back "what was the tone for?".

    You can definitely hear a lot of info in a pure tone as it gets mangled... but many people don't give it a chance.

    I'm not discouraging the use of sine wave tones at all... but I have observed that many people find it difficult to hear when they become distorted from being over driven at some stage. It's certainly a great exercise to trace one along a circuit


    In any event the pertinent thing is too learn to bypass plug ins and patches and isolate and trouble shoot... which just takes some practice, but you are 80% there by asking the question and thinking about it. The rest will be easy.

    best regards,
    mike



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    bitflipper
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    Re:Question about Pure Tone Testing 2011/03/02 12:30:25 (permalink) ☄ Helpful
    The problem isn't the test tone - there are lots of downloadable test tones available online (use 32-bit files <= -6db) - the real challenge is measuring distortion. You can add an awful lot of distortion to a sine wave before you start to hear it, because your brain is simply filtering it out as extraneous information. The same amount of distortion in a complex waveform such as music would be noticeable, but impossible to quantify objectively.

    There is software for generating tones and accurately measuring distortion, but it's expensive. Fortunately, if you don't need precise values you can use SPAN. I prefer version 1 for these kinds of purposes.

    Here's what a 1KHz (-6db peak) distortion-free sine wave looks like:



    After inserting a distortion plugin:



    Of course, in this example the harmonics are huge and easy to see. If you're testing a plugin that you suspect may be introducing far more subtle distortion, you may need to adjust the display scale to see it. If you can't see it on the higher zoom levels, then it's highly unlikely you can hear it, either.


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    The Maillard Reaction
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    Re:Question about Pure Tone Testing 2011/03/02 13:34:28 (permalink)
    I wish we lived near to each other... we could have a web cast.

    best,
    mike


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    Jeff Evans
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    Re:Question about Pure Tone Testing 2011/03/02 15:25:38 (permalink) ☄ Helpful
    meh I am not trying to bestow confusion on you at all. I teach sound engineering (among other things) and probably one of the few forum members here that actually do that. In the end Mike said to drop the tones down to a reasonable level which is excatly what I said. But what level you might say? -14 db is good comprimise. Be aware as the Sonar meters in rms mode will show -17 for a -14 db test tone.

    I think test tones are best for calibrating levels in a system rather than trying to find a stage that might be adding distortion. Level calibration is an area where many do not have any reference or standard. The K system is not just about calibrating monitor levels. It is also very much about a standard for rms levels on tracks and busses and calibrating the monitor system as these K system reference levels are changed. You don't need to get bogged down in K system as you are just trying to find a plugin that might be causing distortion after all.

    Mike pointed you to the article that was Part II.  It is generally a good idea to read Part I first of you are keen.

    http://www.digido.com/level-practices-part-1.html

    Pink noise is also not bad for calibrating levels as well. (tones are better) In my system the pink noise is exactly -1db down from the sinewave tones and it is the same right throughout the signal chain. But you would have a difficult time trying to hear distortion over a pink noise sound.

    As Dave correctly points out sinewave tones are not great for tracking down distortion. You would be better off using a high quality music track as Mike suggests but make it one that is not heavily mastered for volume wars either. Although you can turn your track fader down if you are using a very loud track, it is better to get the actual track (or tone) at the right level to start with. (You will see why when you look at the signal flow diagram of Sonar)

    It is a good idea to study the signal flow of a DAW like Sonar and see what is really going on. It is in the manual somewhere.

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    meh
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    Re:Question about Pure Tone Testing 2011/03/02 17:01:16 (permalink)
    Good answers all ...
    I have read the releated web sites that you all have cited and gained a wealth of new knowledge.  Thanks for the hint bitflipper for the analyzer plug-in.  Thanks to drumr for the link to the tones and the associated web site info was very valuable.
    I guess the Physics is what I really enjoy about having a piece of software like this.
    With all of your help I have realized that the distortions I was hearing were in the samples that the plug-ins generate.  The pure tones have helped me to realize this and I understand the signal path much better now.
    Hopefully this will help make me a better recording engineer....
     
    All Good Info
    thx
     

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