1. WinMLS - Acoustical Measurements
Lars H. Morset & Dr. Johan L. Nielsen Morset Sound Development
Trondheim, Norway

2. Introduction General about us and our measurement system
Theory (Impulse Response and MLS)
Structure of the software
Sound system calibration measurement example
Room Acoustics
Parameters according to ISO 3382
Perform demonstration measurement
What are your needs in acoustical and vibrational measurement systems?

3. Morset Sound Development
A small Norwegian firm
established 1995, WinMLS work started 1997
Dr. J. L. Nielsen involved in room acoustics part
Good connections with the university acoustics group, consultants and Genelec, Finland.
Purpose
Main: Development and sale of WinMLS
Some consultancy work
Hardware solutions for our customers
Adapting the software for our customers

4. Mission of Morset Sound Development
Morset Sound Development is developing and selling professional windows-based software for integration in user-friendly systems for reliable acoustical measurements (currently based on PC and sound card) at low expense.

5. Why we developed WinMLS?
PC & sound card is inexpensive & open hardware
New measurement methods take over...
New equipment needed
Suited for PC/sound cards (problem: initial time delay)
Existing MLS-systems had weaknesses
MLSSA (1 channel, 12 bits, DOS-based)
Some others: Must go through several steps to obtain a measurement or plot the data.
Not flexible enough for the professional user
Senest i går- idrettshall som ikke ble målt

6. Advantages of WinMLS Flexible, but still User Friendly
Made by acousticians for acousticians
Open: Runs on most sound cards => Flexible and low-cost
Get results after one click
By loading setups (default setups available)
Minimum of tedious procedures required
Support several file formats, measure initial time delay, run from Matlab, calibrated measurements, ...

7. Hardware PCI/ISA-card (2-24 channels) Portable system: Laptop
Fsmax= 215 (48) kHz, 24 (16) bit (SNR>100 dB)
Portable system: Laptop
Built-in sound chip
Good enough quality for several applications
Mini-jack plugs not optimum
USB
An extra box needed
VXPocket PCMCIA card (we sell this card)
2-4 (8) channels
High quality plugs
Selectable Microphone/Line input
2 channel card used by >50 professional WinMLS users
4 channel card is new, has just been tested (synch.)

8. Market Segments Some User Segments
Consultants in Sound Systems/Room Acoustics
Research and Education
Sound System Engineers and Installations
Audiophiles
Each segment need customized interfaces
Do this by using setups
Measurement: all settings relating to performing a measurement
Post-processing: all other settings

9. Using WinMLS2000 Start software, explain setups
Measurement
Post-processing
open example measurement
active plot (settings), active measurement
overlay, solo, …
open several measurements
Glossary of terms in help-file

10. Transfer function (Modulus)
The Impulse Response
Time domain
System
under test t
Unit pulse ( d )
Impulse response of the system i
x(t)
y(t)
y(t) = x(t)*h(t)
Linear system
x', x'' inputs e y', y'' outputs
a x' + b x'' a y' + b y'’
Time-invariant system
x(t-t°) y(t-t°)
Frequency domain 
System
under test
White noise
Transfer function (Modulus)
Y() = X()H()
H() = F[h(t)]
Relationship t  :
Used on permission from N. Prodi

11. MLS (Maximum Length Sequence) Method
DETERMINISTIC SEQUENCE MADE OF ZEROS AND ONES WHICH IS TERATED TO IMPROVE THE S/N
TO FULLY EVALUATE THE REVERBERATION TAIL THE SEQUENCE SHOULD BE LONGER THAN THE SUPPOSED REV. TIME.
THEORY
x(n), y(n) discretized signals
R correlation operation
Rxy(n) = Rxx(n) *h(n)
since x(n) = MLS one has
Rxx(n) = (n) (like WN !!)
Rxy(n) = (n) *h(n) = h(n)
h(t)
Generator
MLS x(n) y(n) 6
Hadamard
tramsform
Correlation
input - output 6
h(n)
Maximum length of the impulse response
MLSSA max order points s*
WinMLS max order > points s *
*sr = 44.1 kHz
Used on permission from N. Prodi

12. Emphasis to improve SNR

13. Frequency Resolution Displayed freq res = Sample rate / FFT Size
Sample Rate = 48 kHz
FFT Size = 214 = 16,384 points
Displayed freq res = 48k / 16k = 2.93 Hz
Impulse resp length = MLS period / Sample rate
MLS Period = = 16,383 points
Impulse resp length = 16k / 48k = 341 ms
True frequency resolution = 1 / Imp resp length
True frequency resolution = 1 / = 2.93 Hz

14. Time Windowing
Used to remove room reflections from the impulse response when computing Frequency Response
Different shapes
Full, Half, (Flat top)
Rectangular, Cosine, Hanning, Hamming, Blackmann-Harris, Kaiser-Bessel and others
New True freq res = 1 / Window imp resp length
New true frequency resolution = 1 / = Hz
Demonstration of time windowing in WinMLS...

15. “Radiation” Setup Radius 1.05 m (far field)
Resolution 22.5 degrees -> 1.5 kHz is limit for measuring directivity.
Fast (15 min) using 8-channel MLS and PC-controlled turntable.
Automatic method for saving makes this possible