Jade 2 Technical Support

Frequently Asked Questions


Data Capture
Calibration
Viewing Charts
Sound Card
General


Data Capture

Why are time weightings not stored in the meter library?

Jade 2 samples the raw data from the meter before the meter's own time weighting has been applied. As a result, the time Weighting setting on the meter is not used (and can be set to Fast or Slow as desired for convenience).

What are the time weightings in the Data Capture dialog?

When Jade 2 calculates the Lp values for storing in the data file, it uses a time weighting. The two time weightings provided are the standard ones of Fast and Slow (with a time constant of 125 milliseconds and 1 second respectively). Note that these time weightings are independent of any time weighting set on the meter. For most purposes, the Fast setting is preferred. However, certain statistics, such as Losha and Ldod, require the Slow setting.

Which data types have a time weighting applied?

Jade 2 calculates its own time weighting by software for Lp data during data capture. By definition, Leq and Lpk data are not time weighted.

Which data types have a frequency weighting applied?

All data generated by Jade 2 has a frequency weighting applied by the meter. Note that the main effect is that the Lpk value is the weighted peak value. Jade does not attempt to remove or adjust the frequency weighting. Of course, if the meter is set to unweighted/Linear, the data generated by Jade will also be unweighted/Linear. Note that some meters have both a weighted and unweighted AC output, so you should use the appropriate one.

Why doesn't Jade use a simple microphone instead of a sound level meter for data capture?

The main reason is that sound level meters provide a low-cost way of obtaining a frequency weighted signal. They also handle the range shifting necessary to cover the usual range of levels from 30 to 130 dB (16-bit sound cards can only cope with a 70dB range with a reasonable resolution). Simple microphones provide none of these advantages and cost at least as much as the cheapest meters.


Calibration

What is the distortion figure in calibration?

The distortion figure is calculated by comparing the energy received during complete cycles of the calibration tone with the theoretical energy that should be received from a pure sine wave of the same frequency. On the assumption that the calibrator produces a pure sine wave, it is an indication of how well the sound card is handling the signal.

What is an acceptable distortion level?

A good sound card should give a distortion level of 3-15%. Note that, in particular, the distortion will inevitably be higher if the sound card is only sampling at 11KHz rather than 22KHz or 44KHz. It will also be higher if the calibration frequency is lower than the standard frequency of 1KHz.

Why do I get a high distortion level?

An extremely high distortion (25% plus) may be caused by one of the following:

  • Failing batteries in the meter, calibrator or both.
  • A loose connection in the cable between the meter and sound card.
  • A low quality calibrator that produces an impure tone (e.g. a clipped square wave rather than a sine wave). This may also be the case if you use an internal calibrator built into a meter.
  • A cable with incorrect values for the attenuation resistors, or with no attenuation resistors.
  • A damaged sound card :-(

Why does the calibration process continue beyond "OK" into "High" or "Over"?

During the first calibration, Jade tries each volume setting on the sound card in turn. For each level, it records various pieces of information, including the distortion level and worst case resolution. Once it has tried all possible levels, it then chooses the best level using the previously recorded information. The status information in the gauge is provided primarily for feedback purposes and to alert the user in case all the levels are "Under" or "Over". "Low", "OK" and "High" are all acceptable. It is perfectly normal to see the gauge showing all levels. In addition, this first calibration may take several minutes, especially if you have a high quality sound card that has a large number of possible volume settings.

On subsequent calibrations, Jade tries the previously recorded sound card setting first. Only if this is unsuitable does it then try all the other settings, as with the first calibration. Subsequent calibrations are therefore much faster.

Why is my calibration producing strange results?

Firstly, double check that all the connections are secure. Then check that all the batteries are fresh. We have found that meter/calibrator battery level indicators are not always 100% reliable at detecting the battery end point - they may indicate that the battery is OK and the battery then fails a few minutes later. Calibration can be susceptible to errors introduced by a marginal battery level. Also, if possible, check that the calibrator is producing a sine wave and not a distorted signal. If calibration works with another calibrator, you will know that the calibrator is at fault.


Viewing Charts

What is the home level?

The home level on a chart is the zoom level at which the data does not need to be averaged together (that is 1 chart point = 1 data sample). At this zoom level, the status bar reads "Real". Zoom levels below the home level simply magnify the chart. Zoom levels above the home level apply some sort of averaging algorithm to the data. For example, Leq is combined into larger Leqs, Lp samples are dropped and for Lpk samples the highest value is taken. The status bar shows the averaging algorithm used.

Why do I see different levels when I zoom in?

When you zoom into a level above the home level, Jade recalculates the chart using the new chart point interval. As a result, the values displayed will almost certainly be different to those at the higher level. However, in all cases, the chart points are the appropriate values for the chart interval used. Only at zoom levels at or below the home level is a simple magnification of the chart used.

Why doesn't a landscape printout occupy the entire width of the page?

Jade prints a chart using a WYSIWYG algorithm. In other words, it tries to match the printed image to the image on the screen. If you have a squareish chart window, the chart printout will also be squareish - on a landscape printout this will not occupy the entire width of the page. To obtain an optimum landscape printout, you should first resize the screen image to be landscape in proportions too. Note that hiding and showing the statistics also affects the proportions of the printed chart.

Where are the times taken from in charts?

In common with most charting programs, Jade takes the time for a point as the time at the start of the point.


Sound Card

What is the difference between resolution and accuracy?

Resolution is literally the resolving power of a system, that is the smallest increment in a measurement answer. For example, a voltmeter could have a display in units of millivolts, but (because it is a cheap meter :-) ) could give answers that vary by a tenth of a volt from the international standard values. In this case, the meter would be said to have a resolution of 1 millivolt, but an accuracy of ±100 millivolts.

Current sound cards use 16-bit data capture. 16 bits means that the sound card will produce a result from -32768 to +32767. Theoretically this corresponds to a 90dB range. However, the bottom step from a count of 1 to a count of 2 corresponds to a 6dB increment. As a result, Jade limits the range used to a maximum of about 70dB, which usually results in the worst case resolution of ±1dB. The best case resolution is ±0.1dB. The accuracy of Jade is determined by a number of factors:

  • The accuracy of the sound level meter's AC output.
  • Distortions introduced by the cable and/or sound card.
  • Errors introduced during calibration.
  • Rounding during calculations.

Providing that the sound level meter, calibrator, sound card and cable are of a sufficiently high quality, these should not contribute significantly to measurement errors.

Does a 32-bit sound card give me better results?

To date, as far as we are aware, most so-called 32-bit sound cards still provide a 16-bit data capture section. The 32-bit in their name refers to the wave table and other playback capabilities - this is great news for games and music making but doesn't help with recording noise. Currently, therefore, a 32-bit sound card will be no better or worse than a 16-bit card. In our opinion, you are better spending your money on a high quality 16-bit card, such as the ones produced by Turtle Beach.


General

What are the TXO files?

TXO files are compiled scripts. These are used for two main purposes in Jade: generating the measurement details note and exporting data. If you are interested in writing your own export formats, or a customized measurement details note, please contact us for assistance.