ARTA

User Manual

Ivo Mateljan

Content

1 Introduction

1. Impulse response measurement system with signal generators: periodic white noise, periodic pink noise, MLS, linear and logarithmic swept-sine.
2. Dual channel Fourier analyzer with signal generators: white noise, pink noise, periodic white noise and periodic pink noise.
3. Single channel Fourier analyzer with signal generators: periodic white noise and periodic pink noise.
4. Spectrum, octave band and THD analyzer with signal generators: sine, two sine, multitone, white noise, pink noise, periodic white noise and periodic pink noise.
5. Triggered storage scope with gated spectrum analysis and short-time Fourier transform.
6. Two-channel voltage level meter and third octave analyzer.

1. Integrating SPL meter with 24 hours data logging,
2. Octave SPL meter with noise rating (NR, NC, PNC, RC, NCB),
3. Third octave SPL meter with report of specific loudness, loudness in Sone and loudness level in Phone.

1. Gated frequency response,
2. Smoothed frequency response (in $1/n$$1/n$1//n1 / n-octave bands),
3. Step response,
4. Impulse response envelope (ETC - curve),
5. Cumulative spectrum and burst decay waterfall curves and sonograms,
6. Energy decay in reverberant environments,
7. Room acoustical parameters
8. Speech intelligibility measures: MTF, STI, RASTI, %AL.
9. Loudspeaker directivity pattern

1.1 Requirements

• Operating systems: Windows Vista / 7 / 8 / 10 / 11
• Processor class Pentium, clock frequency 1 GHz or higher, memory 2 GB for 32bit Windows or 4GB for 64bit Windows.
• Full duplex soundcard with synchronous clock for AD and DA converters
• WDM or ASIO soundcard driver (ASIO is trademark and software of Steinberg Media Technologies GmbH).

1.1.1 Soundcards

• standard sound systems that are incorporated in the computer motherboard,
• add-on sound cards for PCI or ISA bus,
• sound systems that connects to the computer USB or Firewire interface.

XLR- female	XLR - male	TRS 6.3mm and 3.5 mm	TS 6.3 mm and 3.5 mm	RCA
(b) D)	$$=T(\text{(})$$$$=T(\text{ ( })$$=T(" ( ")=T(\text { ( })	$=-\mathrm{Crco}$$=-\mathrm{Crco}$=-Crco=-\operatorname{Crco}	$$=\mathbb{C}$$$$=\mathbb{C}$$=C=\mathbb{C}
pin1 - ground pin 2 - plus pin 3-minus pin1 - ground pin 2 - plus pin 3-minus| pin1 - ground | | :--- | | pin 2 - plus | | pin 3-minus |	pin1 - ground pin 2 - plus pin 3-minus pin1 - ground pin 2 - plus pin 3-minus| pin1 - ground | | :--- | | pin 2 - plus | | pin 3-minus |	$$\overline{\begin{array}{rl}& \text{T (tip) - plus}\\ & \text{R (ring) - minus}\\ & \text{S (sleeve) - ground}\end{array}}$$$$\overline{\begin{array}{rl}& \text{ T (tip) - plus }\\ & \text{ R (ring) - minus }\\ & \text{ S (sleeve) - ground }\end{array}}$$[" T (tip) - plus "],[" R (ring) - minus "],[" S (sleeve) - ground "]\begin{aligned} & \hline \text { T (tip) - plus } \\ & \text { R (ring) - minus } \\ & \text { S (sleeve) - ground } \end{aligned}	T (tip) - plus S (sleeve) - ground T (tip) - plus S (sleeve) - ground| T (tip) - plus | | :--- | | S (sleeve) - ground |	pin - plus guard - ground pin - plus guard - ground| pin - plus | | :--- | | guard - ground |
balanced microphone cables	balanced microphone cables	balanced cables or unbalanced stereo cables	unbalanced cables (coaxial cable)	unbalanced cables (coaxial cable)

XLR- female XLR - male TRS 6.3mm and 3.5 mm TS 6.3 mm and 3.5 mm RCA (b) D) =T(" ( ") =-Crco =C https://cdn.mathpix.com/cropped/2024_11_11_011ef5e01945c08a0700g-006.jpg?height=70&width=216&top_left_y=2172&top_left_x=1587 "pin1 - ground pin 2 - plus pin 3-minus" "pin1 - ground pin 2 - plus pin 3-minus" " T (tip) - plus R (ring) - minus S (sleeve) - ground " "T (tip) - plus S (sleeve) - ground" "pin - plus guard - ground" balanced microphone cables balanced microphone cables balanced cables or unbalanced stereo cables unbalanced cables (coaxial cable) unbalanced cables (coaxial cable)| XLR- female | XLR - male | TRS 6.3mm and 3.5 mm | TS 6.3 mm and 3.5 mm | RCA | | :---: | :---: | :---: | :---: | :---: | | (b) D) | $=T(\text { ( })$ | $=-\operatorname{Crco}$ | $=\mathbb{C}$ |  | | pin1 - ground <br> pin 2 - plus <br> pin 3-minus | pin1 - ground <br> pin 2 - plus <br> pin 3-minus | $\begin{aligned} & \hline \text { T (tip) - plus } \\ & \text { R (ring) - minus } \\ & \text { S (sleeve) - ground } \end{aligned}$ | T (tip) - plus <br> S (sleeve) - ground | pin - plus <br> guard - ground | | balanced microphone cables | balanced microphone cables | balanced cables or unbalanced stereo cables | unbalanced cables (coaxial cable) | unbalanced cables (coaxial cable) |

• Standard PC soundcards use stereo cables and mini-TRS connectors (Fig. 1.1).
• Semi-professional high quality soundcards use RCA connectors and unbalanced connections (Fig. 1.2).
• Professional soundcards use TRS 6.3 mm connectors for balanced connection, TS 6.3 mm connectors for unbalanced connection, and XLR (Cannon) connectors for balanced microphone connections (Fig 1.3).
  

  

1. Line-In (light blue)
2. Line-Out - Front speaker (green)
3. Mic In - Mono microphone (pink)
4. Out - Central speaker and Sub-bass (orange)
5. Out-Back speaker (black)
6. Out - Side speaker (grey)
   

   

Figure 1.1 Audio connectors on the PC motherboard (example for $5+1$$5+1$5+15+1 surround sound system).
Standard PC stereo systems have three connectors ( 1,2 , and 3 on the motherboard). Surround 5+1 sound systems have additional three connectors ( 4,5 , and 6 on motherboard). One of the outputs is designed to drive headphones with nominal $32\mathrm{\Omega }$$32\mathrm{\Omega }$32 Omega32 \Omega impedance. For soundcard testing we will use loopback connection of Line-In (blue) and Line-Out (green) using stereo cable terminated with miniTRS connectors. Input impedance of Line-In input on most PC soundcards is $10-20\mathrm{k}\mathrm{\Omega }$$10-20\mathrm{k}\mathrm{\Omega }$10-20kOmega10-20 \mathrm{k} \Omega.
On laptops and notebooks, usually there are only headphone output and microphone input. Those systems are not appropriate for use with ARTA, as they cannot enable measurements in dual-channel mode because microphone input is a mono channel.

Figure 1.2 PCI card with RCA connectors (i.e. Terratec EWX24/96 or M-Audio Audiophile 24/96). There are separate connectors for left channel (in white color) and for right channel (in red color).

1.2 Measurement Setup

1. Dual channel measurement setup
2. Single channel measurement setup
3. Semi dual channel measurement setup
4. Loopback for soundcard testing

A general measurement setup for system testing is shown in Fig. 1.4. The soundcard left line-output channel is used as a signal generator output.
The left line-input is used for recording a D.U.T. output voltage and the right line-input is used for recording a D.U.T. input voltage. In a single channel setup, only a D.U.T. output voltage is recorded.
In a semi dual channel setup the right line-input is used to measures the right line-output voltage. In a loopback setup, the left line-output is connected to the left line-input and the right line-output is connected to the right line-input.

Setups for acoustical measurements are shown in figures 1.5, 1.6, 1.7 and 1.8.

To protect the soundcard input from a high voltage that may be generated by the power amplifier, it is recommended to use a voltage probe circuit, as shown in Fig. 1.6. Values of resistors R1 and R2 have to be chosen for arbitrary attenuation (i.e. $\mathrm{R}1=8200\mathrm{\Omega }$$\mathrm{R}1=8200\mathrm{\Omega }$R1=8200 Omega\mathrm{R} 1=8200 \Omega and R2 $=910\mathrm{\Omega }$$=910\mathrm{\Omega }$=910 Omega=910 \Omega gives probe with -20.7 dB $(0.0923)$$(0.0923)$(0.0923)(0.0923) attenuation if the soundcard has usual input impedance $-10\mathrm{k}\mathrm{\Omega }$$-10\mathrm{k}\mathrm{\Omega }$-10kOmega-10 \mathrm{k} \Omega ).

Figure 1.6 Voltage probe with soundcard input channel overload protection

Figure 1.7 Single channel measurement setup for acoustical measurements

Figure 1.8 Semi-dual channel measurement setup for acoustical measurements

ARTA is also targeted for “point-to-point” testing of audio quality in communication systems. Figure 1.10 shows setup for testing such systems. Interface to mobile phones can be realized by using a headset I/O. Interface to the standard phone line (POTS) is shown in Fig. 1.11.

Figure 1.10 Measurement setup for testing communication systems

1.3 A First Touch

When you start ARTA you will see the program window as shown in Figure 1.12. This window is called Impulse response window (Imp window). It will be primarily used to show the impulse response, also it will be used to show the time record of captured signals.

• Dual channel frequency response measurement window
• Single channel frequency response measurement window
• Spectrum analyzer window

Now click these menus or toolbar icons to see how the measurement windows are working.

Figure 1.13 Dual-channel frequency response window - FR2 (the single channel frequency response window - FR1 looks the same)

1.4 Audio Devices Setup

Before you start measuring you have to setup your hardware and audio devices by clicking the menu Setup->Audio Devices or by clicking the toolbar icon $\mathbf{△}\mathbf{0}$$\mathbf{△}\mathbf{0}$/_\0\boldsymbol{\triangle} \boldsymbol{0}. You will get the dialog box for the audio devices setup shown in the Fig. 1.15.

In section External preamplifier:

1.4.1 WDM Audio Driver Setup

1. Click on channel info to choose the playback channel. It is not recommended to use the measurement channel as a default audio channel.
2. Click on button ‘Properties’ to opens channel ‘Sound properties’ dialog.
3. Click on the tab ‘Levels’ to open the output mixer (as in Fig. 1.17). Then mute Line In and Mic channels, if exist.
4. Click on the tab ‘Advanced’ to set the channel resolution and a sample rate (as in Fig. 1.20)
5. Repeat previous procedure 1) to 4) for recording channel and choose the same sampling rate as in the playback channel.
   

   

Figure 1.16 Sound Control panel

Figure 1.17 Playback channel properties - Output levels

1.4.2 ASIO Driver Setup

ASIO drivers are decoupled from the operating system control. They have their own control panel to adjust native resolution and memory buffer size. The buffer is used for the transfer of sampled data from the driver to the user program.
User opens the ASIO control panel by clicking button ‘Control Panel’ in ARTA ‘Audio Device Setup’ dialog. Fig. 1.19 shows an example of ASIO control panel.

1.5 Calibration

Menu command Setup->Calibrate devices opens the dialog box ‘Soundcard and Microphone Calibration’ shown on Fig. 1.22. That dialog enables setup of sensitivity for soundcard input and output channels. The same dialog box serves for calibration of microphone sensitivity.
Microphone sensitivity defines mapping of sound pressure on microphone membrane to voltage generated by microphone. It has unit mV/Pa.

1.5.1 Calibration of Soundcard Output Left Channel

1. Connect the electronic voltmeter to the left line output channel.
2. Set ‘Output level’ control to -3dB or less.
3. Click the button ‘Generate sine ( $\mathbf{4}\mathbf{0}\mathbf{0}\mathbf{H}\mathbf{z}$$\mathbf{4}\mathbf{0}\mathbf{0}\mathbf{H}\mathbf{z}$400Hz\mathbf{4 0 0} \mathbf{~ H z} )’ and program generates output sine signal with peak value that is 3 dB below full scale value (or other value set with Output level control). The button label changes to ‘Stop generator’.
4. Enter the voltmeter readout in edit box (in $\mathbf{m}\mathbf{V}\mathbf{r}\mathbf{m}\mathbf{s}$$\mathbf{m}\mathbf{V}\mathbf{r}\mathbf{m}\mathbf{s}$mVrms\mathbf{m V} \mathbf{~ r m s} ). (Note that rms value is 3 dB , or 1.414 times, lower than peak value). If you read the peak value from scope in the combo box choose ’ mV peak’.
5. Click the button ‘Stop generator’, then click the button ‘Estimate Peak Output mV’.
6. The estimated value will be shown in the box ‘Estimated’. Following equation is used for sensitivity:

1.5.2 Calibration of Soundcard Input Channels

1. Set the left line input volume to some value. Start with maximum volume or minimum gain if your soundcard has a built in preamplifier. Later you can calibrate for different preamplifier gain.
2. Connect the left output to the left line input channel.
3. Click the button ‘Generate sine ( $\mathbf{4}\mathbf{0}\mathbf{0}\mathbf{H}\mathbf{z}$$\mathbf{4}\mathbf{0}\mathbf{0}\mathbf{H}\mathbf{z}$400Hz\mathbf{4 0 0} \mathbf{~ H z} )’ and monitor the input level at bottom peak-meters. If the soundcard input is clipping, lower the level of input volume. Alternatively, you can lower the generator level (but, then you need to measure output voltage Vrms again).
4. Enter the value of generator voltage in the edit box (but only if it differs from value used during output channel calibration (1.5.1)).
5. Click the button 'Estimate Peak Input $\mathbf{m}\mathbf{V}$$\mathbf{m}\mathbf{V}$mV\mathbf{m V} ', and program calculate sensitivity as ratio of Vrms / Drms.
6. If you are satisfied with measurements, click the button ‘Accept’, and estimated value will become the current value of the ‘LineIn Sensitivity’.
7. Repeat steps 1-6 for the right input channel.

1.5.3 Calibration of the Microphone

1. Connect the microphone preamplifier to the soundcard input (left or right).
2. Enter the preamplifier gain.
3. Attach the sound calibrator on the microphone.
4. Press the button ‘Estimate mic sensitivity’.
5. If you are satisfied with a measurement, press the button ‘Accept’.

1.5.4 Frequency Response Compensation

microphone mb550
freq(Hz) Magn(dB)
48.280 0.34
48.936 0.28
49.601 0.21

. . . .

1.6 Rotating Turntable Driver Setup

1. External .exe file DIY-turntable driver,
2. Internal driver for Outline turntable ET 250-3D
   

   

1.6.1 External .exe file driver

1. First type of command has an argument denoted -r and it resets turntable and sets current position as zero angle position.
2. Second type of command has argument an integer in range - 360 to 360 and it represent a command to rotate turntable to angle given by that argument.

1.6.2 Internal driver for Outline turntable ET 250-3D

1.6.3 Testing of turntable driver

1. Resetting turntable is done by pressing the button ‘Set current position as zero degree position’.
2. Rotating turntable to angle (value -360 to 360 ), that is entered in the edit box, is done by pressing the button ‘Rotate to angle’.

1.7 Getting Images of Graphs and Windows

Images of graphs and windows can be copied to Windows clipboard or saved to the file in a three image formats: .png, .bmp and .jpg. It is recommended to use .png format.
Obtaining copy of the full window picture is simple. The user needs to simultaneously press keys Ctrl+P. After that command the window picture will be saved in the System Clipboard. From there the user can paste it in other opened Windows applications (MS Word, MS Paint).
Keys Ctrl+Alt+P activate command to save that image in the file.
To copy or save the graph picture, that is shown inside the window, user needs to simultaneously press keys $\mathbf{C}\mathbf{t}\mathbf{r}\mathbf{l}+\mathbf{C}$$\mathbf{C}\mathbf{t}\mathbf{r}\mathbf{l}+\mathbf{C}$Ctrl+C\mathbf{C t r l}+\mathbf{C} or activate the menu command ‘Edit->Copy’, or press appropriate ‘Copy’ button. In the main window toolbar, the ‘Copy’ button is shown as toolbar icon 1 .

1. By using the combo box above ‘OK’ button, user chooses one of three modes of saving the image: Copy to Clipboard, Save to File and Save to File + Copy to Clipboard.
2. In the Edit box user optionally enters the text that will be appended at the bottom of the graph.
3. Check box ’ Add filename and date’ enables adding text to the graph that shows file name, date and time. If overlay curves exist their names and line color signs are added at the bottom of the graph.
4. Check box ‘Save text’ enables saving entered text for the next copy operation.
5. Combo box ‘Aspect ratio’ enables copying of graphs with fixed aspect ratios: 3:2 and 2:1.
6. Bitmap size is chosen by selecting one of following combo box items:

• Current screen size - user adjusts graph width and height
• Smallest - graph width is 500 points
• Small - graph width is 600 points
• Medium - graph width is 800 points
• Large - graph width is 1000 points
• X Large - graph width is 1200 points
• XX Large - graph width is 1500 points
• XXX Large - graph width is 2000 points

2 The Spectrum Analyzer

2.1 Soundcard testing

1. Make the loopback connection for the soundcard testing.
2. Click the menu Mode -> Spectrum Analyzer or click the toolbar icon SPA.
3. Click the menu Generator->Setup or click the toolbar icon $\sim$$\sim$∼\sim. You will get the dialog box shown in Fig. 2.1.
   

   

The same parameters can be set up in a dialog box ‘Spectrum Analysis Setup’ shown in Fig. 2.2. (you get it by clicking the menu Setup->Measurement). By using this dialog box you set (1) the preferred input channel, (2) averaging parameters and (3) the FFT resolution.

Input channel section:

5. Choose: Input channel: Left.

6. Prepare the Windows sound mixer:

• Enable the line-input channel
• Mute the line-input channel in the output mixer.
• Set the line-out volume for maximum output sensitivity.
• Set the line-input volume near minimal input sensitivity.

7. By menu command Setup->Spectrum Scaling ( $\overline{\mathrm{ABC}}$$\overline{\mathrm{ABC}}$bar(ABC)\overline{\mathrm{ABC}} ), or by clicking right mouse button in graph title area, you get the dialog box ‘Spectrum scaling’ (shown in Fig. 2.3). Use this dialog box to set (1) the magnitude scaling, (2) the power weighting and (3) distortion measures.
   

   

Scaling section:
    Magnitude scaling: dBFS (dB re full scale),
                        dBV or SPL (sound pressure level),
                        PSD (power spectral density mode in dBV/\sqrt{}{Hz}\mathrm{ ).}\\mathrm{ .}.
    Voltage units: dBV or dBu,
    Pressure units: dB re 20u Pa or
        dB re 1 Pa (valid only if microphone is connected and enabled).

Power section:

Distortion section:

Slowly increase the volume of the line input channel (using the soundcard mixer) until you get the peak level close to -3dB FS.

If you get THD+N lower than $0.1\mathrm{\%}$$0.1\mathrm{\%}$0.1%0.1 \% you have a usable soundcard.

2.2 The Spectrum Estimation Procedure

1. An input signal is sampled with frequency $f_s$$f_s$f_(s)f_{s} and transformed into discrete sequence $x_n$$x_n$x_(n)x_{n} of length $N=FFT$$N=FFT$N=FFTN=F F T size (the number of samples in the acquisition window is equal to the ‘FFT size’, and can be set to: 4096, 8192, 16384, 32768, 65536 or 131072).
2. The discrete input sequence is multiplied with a window sequence $w_n$$w_n$w_(n)w_{n} (will be explained later)
3. The Discrete Fourier Transform

4. The magnitude spectrum is shown in one of following scaling modes:

• RMS - RMS level of an input signal - defined as $10{\log }_{10}$$10{\log }_{10}$10log_(10)10 \log _{10} (sum of all DFT power spectrum components).
  If the power weighting, in the ‘Spectrum Scaling’ dialog box, is set to A, B or C filter, then each spectral component is weighted, before the spectrum summation, with a magnitude response of A, B or C filters (for definition of these filters see section 2.4).
• THD - total harmonic distortion - defined as percentage of the square root of ratio of power sum of higher harmonics $(H_2,H_3,..)$$\left(H_2,H_3,..\right)$(H_(2),H_(3),..)\left(H_{2}, H_{3}, ..\right) to the power of fundamental signal harmonic $\left(H_1\right)$$\left(H_1\right)$(H_(1))\left(H_{1}\right).