Tons of acoustic Services from FORCE Technology

With the merger of DELTA and FORCE Technology, we now provide an even broader range of services and products.

You can see our list of acoustic services here.

and our facilities include access to

  • Anechoic rooms
  • Reverberation rooms
  • SenseLAB
  • Advanced instrumentation
  • Custom signal processing techniques
  • Expert-driven acoustic and vibration troubleshooting workshops

 

Did you know that:

  • For many years we have played a significant role as advisor to the Danish Environmental Agency, helping shape noise measurement techniques.
  • We have pioneered the development of new techniques for the measurement of tones and impulsive noise, based on solid psychoacoustic research. These are now widely used in national and international standards, and also are available in noiseLAB.
  • We work closely with major wind turbine manufacturers in advanced measurements, and develop new noise measurement standards for wind turbines.
  • Advanced noise propagation models (Nord2000) provide for noise mapping applications.  And with new computational techniques are seeing up to 100 times better performance.
Advertisements
Posted in Uncategorized

Transient Analysis Tricks in noiseLAB

Analysis of transient signals requires extra thought and care. The main challenges are:

  1. Avoiding overloads
  2. Editing files correctly to prevent artifacts
  3. Understanding Filter settling times
  4. Properly scaling to make comparisons possible.
  5. 3D Measurements: Spectra as a Function of Time.

Fortunately, noiseLAB Capture and its companion Batch Processor provide significant capabilities for these applications.

Avoiding Overloads

  • Make a trial recording and observe whether noiseLAB Flashes red when overloads occur.  Adjust you input gains, if possible, or choose a less sensitive transducer.
  • If you have Recordings with overload,

Double Transientsuse the Preview graph of the A-Weighted Sound Level (Fast)  on the left graph with Red markers indicating overload. The Level Waveform graph on the right shows the oscilloscope waveform of one second duration after the cursor (Blue) on the Preview graph. Waveform portions on the right graph greater than +-1 are overloaded.

  • you should Edit the Recording to not include these.

Editing to exclude Overloads

Rapid Transients-Precision Editing

The above clip is tricky, because we have to avoid the OVERLOAD.

TRICK 1: You can single step the GREEN (Start) Cursor with SHIFT <Right or Left Arrow>

TRICK 2: You can single step the RED (End) Cursor with CTRL <Right or Left Arrow>

TRICK 3: Step back and forth between peaks using the UP or Down arrow, with the same SHIFT and CTRL tricks.

Adjust Cursors Right Click

TRICK 4: (Shown above) Right click on the Clip name in the Clips listbox, to update the Clip Start and End from the Current Cursor positions. This effectively re-does the edit.

Analysis of Rapid Series of Transients:

BAD TRICK: Do not create short Clips. This can create significant settling issues and errors where performing spectrum analysis.

Settling time of Octave Filters

GOOD TRICK:  noiseLAB always shows the settling time of 1/3 octave (also 1/N octave) filters. These are shown in the Result listbox in the Filter Settled column. There are two cases:

  • Normal analysis of a Recording or Clip:  noiseLAB automatically resets the RMS averaging when the filters have settled. Thus the final averaged result is correct, but is of shorter duration than the actual clip. noiseLAB shows the actual settling time at the beginning which is not included in the analysis.  This must be subtracted from the Duration to give the actual analysis time.

Third Octave Filter Settling

  • Time Slice Analysis (in the Batch Processor): One or more of the first Time Slices may not be settled. Note that after 1 second, the Results list box shows all the following slices are settled:

SettledThirdOctaveSlices

Results with filters that are not settled are incorrect and must not be used.
The filter settling time is determined by the Bandwidth of the lowest frequency filter in the Octave Analysis.

The settling time is approximately as follows:

T = 5 / Bandwidth                                     (Formula 1)

The Bandwidth of a Third Octave Filter is 23% of the Center Frequency.
So if the lowest center frequency in your third-octave analysis is 20 Hz, then the filter bandwidth is 4.6 Hz, and the Settling Time is about 1 second.

Broader filters, such as 1/1 Octave filters settle more quickly, and more narrow filters such as 1/6 to 1/24 Hz settle proportionately more slowly.  In all cases, noiseLAB reports the settling time.

To optimize settling times, noiseLAB Batch provides several low frequency cut-off choices. noiseLAB first reports Settled as True, when all filters have settled.

To intuitively better understand the response and settling characteristics of octave filters, we can compare them to a stringed piano, where the spacing between the keys is 1/12 octave.  The longer the string, the deeper the tone, and the more sluggish the response, and also, with a longer settling time.   Bass strings can “sing” a long time, whereas high tones are very short duration and very “stacatto”.

Scaling of Octave Measurements

To make a valid measurement of transient signals, one or more transients must be fully contained in a single Clip or slice, and all filters must have settled.

To make comparisons possble you must the normalize the dB value to 1 second duration.

For example if you want to find the average transient level of 10 transients in a 100 second recording, you measure the 1/3 octave level over the 101 seconds (to make the math easy), and subtract 1 second for the settling time.

  • You then correct the duration to a normalized 1 second, by adding 20 dB.
  • And to get the average level of the individual 10 transients you subtract 10 log N, where N is the number of transients.

The formula for calculating the average, normalized energy of N transients is:

dB (n=1, t=1) = 10 (log (T/N))                        (Formula 2)

Where T is the analysis time in seconds

N is the Number of transients.

The same formula applies for normalizing and averaging the Level of Transients, and corresponds to computing LE or SEL as it previously was called.

For FFT Measurements the above formula, and in addition, the normalization to 1 Hz bandwidth must also be included, and the measurement must use a Hanning weighting and an overlap of 66.6% or 75% to ensure a ripple free time domain weighting.

Sound Level Measurement

noiseLAB Analysis results show the Sound Level in 125 ms intervals.  This applies for Fast, Slow, or Custom Exponential time constants. However, internally, noiseLAB samples the RMS detector 500 times per second, to ensure it captures the correct Maximum or Minimum values in each 125 ms interval.

For a rapid series of transients, this can give a plot which may not show the individual transients we know exist. Even though multiple transients may occur in a single125 ms window, only the highest value will be shown, even with a very short time constant of 2 ms.Confusing graph of rapid transients

However, on the Advanced Tab, you can select High Res Time Base :AdvancedHiResTimeBase

to reveal the individual peaks:

ShortTimeConstant for Repeated

To get the average energy of the peaks, use the Formula 2 above.

To export the Graph use the

SaveTableGraph

Save (Graph icon) button.

  • If Slice is Off, only the whole graph shown above will be exported.
  • If Slice is On, graphs of all slices will be exported.

To save the overall values from the Table below the graph, use the Save (Table icon) button:

TimeSlice2msExpTC

To save a table of the numeric values of the Graph first select the Report Tab and select Level vs. Time and the use the Save (table) button.

Report Time Series AdvanceTab

If Slice is Off, the time series of the Entire Clip will be exported as the selected Result.

If Slice is On, all Slices will be Exported, one slice per column:

SliceTimeSeries

Notes on “Excel” Tables:

  • Data are exported as Tab delimited files.
  • The decimal of the file follows the system settings of the computer.
  • The extension of the file is .xls to make it easier to find with Excel.
    • Because of the Tab delimited format of the file, Excel will come with a caution dialog box when opening it, but will still open it properly.
  • From the tab-delimited data you can post-process for functions such as peak picking using Excel, MatLab or LabVIEW.  Tab-delimited files are the most user-friendly for these tools. For MatLab you should normally export files only using the period . as the decimal symbol.

Psychoacoustic tools for Impulse Analysis

The Nordic method for Impulse Analysis (NT ACOU 112) is selected by using the Impulse function of the noiseLAB Batch Processor.  This Nordic standard is currently on its way to becoming an International Standard.

ImpulseNordicStd

3D Analysis of Spectra as a Function of Time

Using the Slice feature of noiseLAB Batch Processor you can view  individual lines of frequency spectra as a function of time. The finest time resolution is 125 ms.

For the above signals, this is not sufficient resolution to resolve individual transients response, but the varying level of the 5910 Hz frequency selected by the Cursor on the upper graph, is still shown on the lower graph.

FFT 3D

and likewise for the third octave spectrum.

ThirdOctave3D

A final example with two slowly decaying transients whose sound level plot is shown:

Two Slow Decays

Now with FFT Analysis (3 Hz resolution) the first rapid decay of the 1029 Hz resonance:

FFTSlowDoubleDecay 1029 Hz

and the slow dual slope decay at 1188 Hz:

FFTSlowDoubleDecay 1188 Hz

And below the same transient analyzed with third octave analysis:

InitialTransient 1000Hz

The initial impulse above is dominated by 1000 Hz which rapidly decays but is not as clearly differentiated as with the higher resolution of the FFT earlier shown.

The slow decay after 0.25 s is dominated by 1250 Hz as seen below where the leakage of the 1000 Hz component is not as strong.

SlowDecay1250 Hz

You can freely slice in Time and Frequency by moving the respective cursors on the two plots.

These graphs as well as the corresponding tables can be exported as described above.

For more information contact:

Senior Specialist

Carsten Thomsen

ctho@force.dk

Posted in Uncategorized

13 dB lower noise with NI Module 9250

noiseLAB 4 can now support NI 9250 giving about a 13 dB lower noise floor than with NI 9233 or 9234.  The typical A-weighted noise floor with a 50 mV/Pa half-inch instrumentation microphone is about 20 dB (A)

Before you upgrade, please carefully note the following:

  1. The 9250 has two channels instead of four (for the 9233 and 9234)
  2. The 9250 has 2 mA transducer powering (IEPE), and just like the 9233/34, additional powering must be applied to provide the 4 mA for microphones with a 20 dB gain preamp. However, the lower noise of the 9250 significantly reduces the need for the 20 dB preamp gain.
  3. Chassis: Older USB carriers and chassis such as the NI USB-9162 and NI cDAQ NI 9172 cannot be used with the 9250. You must use newer generation chassis such as the
    • NI USB-9171 (one slot)
    • NI USB-9174 (four slots)
    • (NI USB-9178 (eight slots) (The current edition of noiseLAB only supports 8 channels))
    • [Ethernet versions of the above have not yet been tested for compatibility]
  4. Drivers: noiseLAB Capture 4.0 and later must have the National Instrument data acquisition drivers upgraded to DAQmx 14.0 but no higher than DAQmx 17.5. Note: Carefully check any other National Instruments programs you have installed, along with associated NI hardware, to ensure compatibility with the above mentioned range of DAQmx drivers.    Contact National Instruments for detailed information (ni.com).
  5. noiseLAB 3 is not compatible with the above drivers and modules.

DELTA provides paid support to help you in the upgrade process at a price of €300.  Contact Carsten Thomsen at cth@delta.dk.

Posted in Uncategorized

New perspectives for the future…

A cool Danish research proposal…from DELTA, a part of FORCE Technology.

Chip in with your comments on the proposed research proposal (in Danish):

Highlights:

Enhancing or replacing measurements with digital simulation of the entire chain:

  • Sound Sources: Design and function
  • Sound Generation and Propagation
  • Sound Insulation
  • Simulation of human perception of sound and experienced annoyance, based on advanced listening tests.

We envision developing new services for:

  • What will it sound like? (Auralization)  So you can experience the sounds from the simulated sound sources. Imagine hearing a new motorway before it is built, and the impact of various sound barriers.
  • Will I be impacted? (Annoyance GIS map) A real-time map of sound levels and annoyance.  Based on real-time monitoring, as well as historical data and simulation.
  • Shake, rattle and roll: Designing quieter machines by simulating vibration and sound and how to harness these by simulation and test.
  • No more noisy neighbors: Better computer models for building materials and building design— also to reduce how much you dsiturb your neighbors. 😉

As part of a family of the government approved Advanced Technology Group, FORCE Technology is eligible to bid on result-oriented research proposals to advance the state of the art over a broad range of technologies.

Your comments and input will help shape the priority of different research proposals.

Click here to read and add your comments: proposed research proposal (in Danish)

Posted in Uncategorized

Peak measurements in noiseLAB Capture

If you are making A, B, or C-weighted Peak sound level measurements with noiseLAB Capture, please note that Capture does not apply these weightings to the Peak value, and always measures it with the Linear weighting, even if you have selected and A, B, or C weighting.

noiseLAB Batch applies the selected weighting to Peak, as well as to all other sound level types such as Fast, Slow and Impulse.

If you require additional information, you can contact Carsten Thomsen cth@delta.dk.

Posted in Uncategorized

Cure your dB headaches!

Have you ever had trouble adding decibels, and wonder why 0+0=3?

Or if you measure a level of 30 dB and the background noise is 20 dB, how much should you correct the measured value?

What is the free field sound level at 10 meters from a point sound source with a source power level of 98 dB?

How many Pascals is 94 dB?

What is the sensitivity in mV/Pa for a microphone with a sensitivity given as -26 dB re 1V/Pa?

Tab1

What is the Doppler Frequency  Shift of a 1000 Hz tone of a car passing at 5 meters from the observation point at a speed of 10 m/s?

Tab3

What is the measurement accuracy on a random noise signal filtered with a 1 kHz octave filter and averaged for 1 second.

Tab4ErrorCurves

Solve these and many other simple acoustic calculations with noiseLAB Calculator.  It’s free, ad- free, and with no obligations.

Read more here and download for free.

–OK, obviously we wouldn’t object to you sometime purchasing our noiseLAB Pro Software…;-)

 

Posted in Uncategorized

Notes on noiseLAB on Windows 7 and 10

Current Versions of noiseLAB 4.0.4 and noiseLAB Batch Processor 4.1 run on Windows 10.

Please note the following:

  1. noiseLAB assumes placement of your project files under Documents\noiseLAB Pro Projects\.  However, Windows, by default does not permit programs to write in folders placed in the root of the boot drive (normally the C drive). If you have project folders in a folder at the root of the C drive, you must run both noiseLAB Capture and noiseLAB Batch “Run as Administrator”
    • to be able to store results to these locations
    • for noiseLAB to properly remember locations for save and get operations. –Note:  the above considerations do not apply to other drives than the Boot drive.
  2. Windows Scales and fonts and other settings should be set to 100%. To find these settings in Windows 10, right click on your Desktop and select “Display Settings”. On some computers, the appearance may or may not be correct with other scalings than 100%.
  3. A few front panel fonts on the front panel of noiseLAB may be incorrectly sized. To fix this, add the following three lines to the configuration file for noiseLAB Capture file (.ini) also called Configuration Settings:

appFont=”Tahoma” 13
systemFont=”Tahoma” 13
dialogFont=”Tahoma” 13

This may not work properly for all keyboards etc.  Instead try one of the following:

  1. then copy the lines from the attached pdf file into the .ini file: appFont
  2. or edit the .ini file manually and replace the six quotation marks, with those from your native PC keyboard.

 

and paste them into the .ini file.

This .ini file (Configuration file) is located at the following path location:

C:\Program Files (x86)\DELTA\noiseLAB Capture 4.0\

Double click to open the file and add the three lines to the end of the file.  If Windows does not allow you to save the file at its original location, then save it to your Desktop, and drag the file back to the original location, overwriting the original file. It may prompt for Administrator approval when you do this.

Posted in Uncategorized

noiseLAB 4 Power User Course: April 7, 2017

This half-day course will quickly move you from being a beginner to a power user that works efficiently and confidently with noiseLAB.  We show how you can go from calibration to report ready results in less than three minutes.

And if you are an experienced user of noiseLAB, you may be surprised that you may learn many new tips and tricks to make you even more skilled.

  • Shortcuts to speed up your work.
  • Graph use:
    • Advanced  auto scaling,  how to prevent “jumpy” graphs
    • Manual axis setting
    • Cursor grabbing, setting and finding.
    • Graph Size and background color
    • Peak or Valley search
  • High speed editing
    • Choosing channels to clip or exclude
    • Full Screen editing
    • User-defined channels to clip
    • Automatic naming with user-defined templates.
    • Renaming of Recordings and Clips
    • Changing of Time Stamps.
    • Adjusting the duration of clips
    • Clip padding before start and end.
    • Understanding mother-child relationships for Recordings and Clips
  • Calibration
    • “Live” calibration using acoustic calibrator
    • Calibration by “stealing” a known calibration tone value.
    • Calibration by manual entry.
    • Verifying quality of acoustic calibrator
      • Frequency and Amplitude stability
      • Distortion
  • Understanding the “Preview” Graph
    • Functions shown
    • Overload indication
    • Relationship to Clips and Recordings
  • Analysis types
    • Weighting network used
    • Parallel analysis results
    • Performance considerations: How noiseLAB shows you the processing metrics
  • FFT Spectrum
    • What is the allowable block size?
    • Zoom vs. 0.1 Hz maximum resolution
    • Export of FFT to Excel
    • Window choice
  • Octave Analysis
    • 1/1 to 1/24 octave
    • Settling time of filters:
      • How is this indicated
      • What considerations must I take for short Clips.
  • Sound Level
    • Parallel measurements
    • Why noiseLAB often is more accurate that your sound level meters.
  • Wave file import and export
    • Sampling frequencies
    • How to calibrate
    • Maintaining calibration for Exported .wav files.
  • Batch Processor
    • Differences to noiseLAB Capture
    • Time and Frequency Slice analysis
    • Graph exports with documentation: Easy to put in report.
  • Overview of Advanced Topics
    • Tone Analysis
    • Impulse Analysis
    • Sound Quality
    • Vibration Measurements

Course Date: Friday April 7, Aarhus, Denmark. 10.00-14.30

Price per person:  2500 DKK

Course Language: English or Danish depending on course participants

Registration: Send e-mail to Carsten Thomsen cth@delta.dk or contact at 40 82 77 72.

Posted in Uncategorized

New Sound Propagation Software Released.

SPL 2000 is an updated version of exSOUND2000 featuring

  • Greatly improved user interface
  • Updated Sound Source models.

The program is sold as an experimental research tool, and requires that the user has a thorough understanding of the Nord2000 model.

Existing Users can upgrade for €600, and the price for new users is €1300. The program is available from our on-line store

Use code:

SPL2000Upgrade

for the upgrade price.

Software delivery is typically two working days directly from DELTA.

Educational users:  Please contact DELTA directly at cth@delta.dk.

Posted in Uncategorized

noiseLAB for Multi-channel Use

noiseLAB supports up to 8 simultaneous parallel acoustic channels.

The following is a guide to configuring this most economically:

2-4 channels:

  • For a noise floor of about 30 dB(A) use one National Instruments USB 9234 with four active microphone channels.
  • For a noise floor of about 17 dB(A) use a microphone preamp with 20 dB gain and two active channels.  This gain setting requires additional power from the USB 9234, therefore only two channels can be used and each channel must be coupled in parallel to an  unused inputs to get sufficient powering.

4-8 channels (partial synchronization)

  • User two National Instruments 9234.
  • With a noise floor or 30 dB(A) you can use up to 8 channels.
  • With a noise floor of 17 dB(A) you can use to up 4 channels as described above.
  • The two channels in each 9234 are synchronized, but the two 9234 devices are not synchronized between each other.  Hence precise time relationships cannot be determined, since the internal clocks in the 9234s may drift several seconds per day.

4-8 channels (full synchronization)

  • Solution 1: Use two National Instruments 9234 in a CompactDAQ Chassis cDAQ 9174 which synchronizes the two modules.  The powering constraints described above are the same.
  • Solution 2: Use the National Instruments PCI 4474 (four channels) or PCI 4472 (8 channels)  in a PC with a full size PCI slot.  (Note: PCIe slots cannot be used).   These cards provide 4 or 8 fully synchronized channels, and 8 dB greater dynamic range than the NI 9234.  In addition, each channel provides sufficient powering to drive preamps with 20 dB gain.  Finally, twice as high sampling frequencies as the 9234 are supported.

Notes:

  • Two USB digitizers connected to  noiseLAB must be identical and configured with the same sampling frequency.
  • The 9233 is NOT recommended since it cannot turn off its IEPE powering, and also has  “end of life” status at National Instruments.

 

Posted in Uncategorized