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  • #16

    Does this device come with certification / calibration paperwork of any sort?

    Nope, at least not the PAA3 doesn't. There are no tolerances on the published specifications. It's a tool, not a lab instrument. You take it along on a PA job or a room assessment. You don't use it to determine if you need to sue the factory for too high a noise environment or the airline for flying too close to your house.

    That's why it only costs a few hundred bucks, I guess.
    --
    "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
    Drop by http://mikeriversaudio.wordpress.com now and then

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    • #17
      I think Mike has described it pretty well. The PAA6 is for general testing and ringing out of studios and PA systems, and in that respect, I have to say that it correlates really well with what I'm hearing...not sure I need more accuracy than what it has to tune a room, check performance, and uncover out of phase wiring in speakers
      _____________________________________________
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      • #18
        I should also add...I'll be away from the studio for the next 10 days doing the AES video thing, so I won't be posting on the PAA6 for a bit.
        _____________________________________________
        There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

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        • #19
          Phonic PAA6: Oscilloscope

          Well I must admit, it's been a while since I fired up my Tektronix Dual-Trace Scope that ruled the world a few decades ago...but now thanks to the PAA6, there's a little audio scope I can hold in the palm of my hand. Let's check it out.

          First off, this is audio range only, so don't expect to check your microprocessor’s clock frequency. Within that constraint, however, it's very flexible. You can look at waveforms from the mic or line ins, and have a considerable range of sensitivities. For example, when measuring dB SPL, you can choose a range of 30 to 100dB SPL, 45 to 115dB SPL, or 60 to 130dB SPL. With dBu, there are four ranges spanning -85dB at the lowest end and +25dBu at the highest. dBv is similarly flexible, from -87.2dBv up to a max of +22.8dBv, again separated into four ranges. For voltage (also with four ranges) you can measure from 43.6 microvolts all the way up to 13.7V.

          You start using the scope by setting up the range and measurement type you want, as well as the desired input. You can also set the time per horizontal division, from 0.33ms per division up to 500ms per division. Higher resolutions make it easier to zoom in on a portion of a waveform to see, for example, something like a spike.

          Unlike a traditional analog oscilloscope, the display is quantized to a limited number of steps (hey, it’s digital!) so if you see a flat line at the top of a sine wave that's zoomed in, you won't know if it's clipping or if there's a limitation in the graphic display. However, as shown in the first attached image, the PAA6 will at least inform you if clipping is occurring on the signal coming into the unit, so at least that variable is out of the way.

          The best part of the PAA6 oscilloscope is that it is a true two-channel triggered scope, and the trigger can come from either channel, or both channels. What this means is that with a repeating waveform, the display re-triggers based on the waveform, thus allowing it to remain stationary in the display. With a non-triggered scope, the waveform tends to "wander," making analysis difficult.

          The second attached image shows a sine wave without triggering. If this was a video, you'd see the waveform going back and forth; the sharp vertical line indicates that the sine wave is being triggered at some arbitrary time that has no relationship to the waveform (or at least, I think that's what's happening - Grant, correct me if needed!).

          Now look at the third attached image. In this, the sine wave is being triggered. The display is stationary, and the representation of the waveform is accurate.

          Of course, looking at sine waves is not necessarily the most creative application for an oscilloscope, but it gets the idea across. You could use this feature to check out the waveforms of virtual synths to see what kind of violence happens to the waveform at really high frequencies, check for "ringing" on a square wave when going through a transformer, determine whether a sawtooth wave is positive- or negative-going, and the like.

          Bottom line: The oscilloscope in the PAA6 is not a laboratory-quality instrument that's going to replace my Tektronix, but it is a convenient, easy, and fast way to check out what's happening with the various audio waveforms floating around a studio.
          _____________________________________________
          There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

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          • #20
            Next up: RT60 analysis. This function displays a graph of a room's reverb decay characteristics, namely, how long it takes for the signal to decay to 60dB of its original strength. But there's more to this than meets the eye; it's also possible to filter the signal (A, B, C-weighted, or flat), and look at the RT60 characteristics for any of 10 selectable one-octave frequency ranges. This is great for several applications, such as seeing how adding damping affects the high-frequency decay time.

            As it turned out, I had a practical application for this function. There's a room in my house with a hard surface that used to be an aviary, and I wanted to try using it as an acoustic reverb chamber. When I clapped my hands in there it sounded pretty good, but I wanted an idea of what to expect in terms of reverb time.

            To use the RT60 function, you first have to decide what you're going to use to generate the trigger signal for measurement. The PAA6's internal noise generator is one option, or set the trigger to external so it picks up the mic sound - then you can use a handclap, balloon popping, starter pistol, whatever. I opted for the handclap approach, because I was looking for a qualitative rather than quantitative measurement (i.e., which had a longer decay time). Ideally you want a really loud signal, but hey, I can clap pretty loud. The first attached image shows the Setup screen, where I'm choosing a Flat filter, the mic input, and an external trigger.

            When you start the process by clicking on Run, the PAA6 measures the background noise (see the second attached image). Click Run again, and then it's time to generate the signal (see the third attached image).

            After you generate the measurement, a graph appears on the display (fourth attached image). You can change the display resolution, zooming in or out so that the graph fills up most of the display. Note the sharp cutoff; this occurs at -60dB, so as you can see, the original signal wasn't all that strong in the first place...but it's good enough to get a sense of the decay time. Also, two lines appear on the display that you can trim to zero in on the numeric readings toward the right part of the display. For example, you can move the yellow line to the 60dB point and get a reading. One thing I don't understand: It seems the numeric RT60 reading is different from the reading shown on the display. For example, the display looks like it's showing about 600ms as the -60dB point, but the numeric readout is showing 1.82 seconds. This may just be a case of pilot error, or some aspect I don't understand - Grant, can you (or someone else) explain what's going on?

            Just for grins, check out the characteristics of a typical hard-tiled bathroom (fifth attached image), which has an RT60 time of around 230ms. As you can see, there's nowhere near as much reverb as the first room I tested, but it does get across the idea that using a bathroom as an acoustic reverb chamber for short decays isn't that bad an idea!
            _____________________________________________
            There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

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            • #21
              This is one of the simplest PAA6 "apps" - it's basically a sound level meter that's like a "designer version" of the classic Radio Shack sound level meter. It measures dB SPL through the microphones, and dBu or dBv through the line ins. There are several measurement ranges, so if clipping occurs, you can simply switch to a less sensitive range. Conversely, if you're measuring really low levels, you can switch to a more sensitive one.

              The first attached image shows the setup screen, where you can choose the input, measurement units, weighting, peak hold time, and response time (response time options are 35, 125, 250, and 1000m)s. The peak hold time options are 05, 1, 2, and 4 seconds. However, the display also shows the highest level that was read as a "Max" reading, so you could leave the meter unattended while it's measuring a noise source, then check back later and see the maximum level that registered. Well, at least in theory: I don't quite understand why the Peak readings can be higher than the Max reading, as shown in the second attached image; perhaps the Max reading is an average. Paging Grant... Of course, you can also reset this maximum SPL level.

              The second screen shot also shows a few other interesting aspects. When dealing with definable tones, you'll get a readout of the frequency just above the field where you specify the measurement unit. Also notice there are Peak and Peak-to-Peak readings, and the meter has low and high limit indications to the left and right respectively.
              _____________________________________________
              There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

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              • #22
                For example, you can move the yellow line to the 60dB point and get a reading. One thing I don't understand: It seems the numeric RT60 reading is different from the reading shown on the display. For example, the display looks like it's showing about 600ms as the -60dB point, but the numeric readout is showing 1.82 seconds. This may just be a case of pilot error, or some aspect I don't understand - Grant, can you (or someone else) explain what's going on?


                Somebody may have to correct me if I'm wrong (I often am), but I think the RT-60 measurement is the time it takes for the signal to decay 60 dB (for example, 1.82 seconds or 1.44 seconds in one of the pictures Craig attached). The results are usually measured using a signal 30 dB over the background noise (otherwise you may be struggling to get a decent trigger sound), so there's a bit of forumulating going on for the actual results.

                On the PAA6, the RT-60 result is calculated from the data that lie between the red and yellow lines onscreen - which, in the case mentioned above, isn't quite a 5 dB decay. You could widen the gap between the two lines a bit to get more accurate RT-60 results.

                Side note on the RT-60: As Craig mentioned, you can filter out particular frequencies, but you don't need to take the measurements all over again to do so. You can take the RT-60 once, then go into the set menu to choose a frequency to filter and the graph/results will be updated.

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                • #23
                  ; perhaps the Max reading is an average.


                  I had to ask about this, but it seems the value of the maximum level is in RMS, while the peak and peak to peak are... well... I'll let a couple of diagrams say what I can't:





                  It refers to voltages here, but the theory should be the same for all measurement units that the PAA6 handles.

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                  • #24
                    Okay, that makes sense...I figured that the max reading was peak, as the other measurements were for peaks. But if it's RMS, of course it would be lower.

                    Seems to me it would be good to have the option to have Max capture either RMS to get an average level, or peak to get the highest attained level. It's only a few lines of code, right?
                    _____________________________________________
                    There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

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                    • #25
                      You can change the display resolution, zooming in or out so that the graph fills up most of the display. Note the sharp cutoff; this occurs at -60dB, so as you can see, the original signal wasn't all that strong in the first place...but it's good enough to get a sense of the decay time. Also, two lines appear on the display that you can trim to zero in on the numeric readings toward the right part of the display. For example, you can move the yellow line to the 60dB point and get a reading. One thing I don't understand: It seems the numeric RT60 reading is different from the reading shown on the display. For example, the display looks like it's showing about 600ms as the -60dB point, but the numeric readout is showing 1.82 seconds.

                      I'm not sure I get how it works either. Perhaps what it's doing is looking at the slope between the red and yellow lines and extrapolating the 60 dB range along the time scale based on that slope.

                      RT60 is kind of a "feel good" measurement like THD. What it doesn't tell you is how the frequencies decay with time. If you were to listen to your handclap after 1.8 seconds (assuming a real world space), it wouldn't sound the same as the initial handclap since some frequencies would decay more than others due to the uneven absorption of the reverberant space. So the best you can do with a simple measurement and display is just take an average (probably RMS) reading at the -60 dB level.

                      A waterfall display with frequency, amplitude, and time on three axes is what really can tell you what the room will sound like. A simple RT60 measurement will tell you if you're in a small room or a large room. Or, knowing (by looking around or pacing it off) what size room you're in, a long RT60 will tell you that you have a lot of reflective surfaces, a short RT60 will tell you that you have a lot of absorbent surfaces. But, as you no doubt have discovered, a room that has good high frequency absorption and poor low frequency absorption will probably have a pretty long RT60 but sound tubby, because all that reverberation time is in the low frequency range.
                      --
                      "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
                      Drop by http://mikeriversaudio.wordpress.com now and then

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                      • #26
                        Actually, it can show 10 one-octave ranges and generate a decay graph for each one of these. As I said at the beginning of the RT60 post, "It's also possible to filter the signal (A, B, C-weighted, or flat), and look at the RT60 characteristics for any of 10 selectable one-octave frequency ranges. This is great for several applications, such as seeing how adding damping affects the high-frequency decay time. Granted a "waterfall" display would be cooler, but I think that's beyond the scope of the display.
                        _____________________________________________
                        There are now 14 music videos posted on my YouTube channel, including four songs by Mark Longworth. Watch the music video playlist, subscribe, and spread the links! Check back often, because there's more to come...

                        Comment


                        • #27
                          Sorry, I guess I must have missed the part about the ten 1-octave ranges. That could be useful. The PAA3 makes only a broadband measurement at whatever weighting you've selected (for everything). It allows you to accumulate a running average of multiple readings.

                          I suppose you'd see some difference if the mic was close to an absorber compared to being in the middle of the room, or the normal listening position.
                          --
                          "Today's production equipment is IT-based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio." - John Watkinson, Resolution Magazine, October 2006
                          Drop by http://mikeriversaudio.wordpress.com now and then

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