Test Your Ears:  User Guide Systeem

What is what.



The Attenuator Unit
From left to right: The yellow Led indicating that there is communication with the PC. the green Led indicating power present (the unit is powered from the USB cable)  The USB connector. It needs a standard cable to the PC. The RJ45 connector is for the connection with the ButtonBox, so DO NOT connect it to a network port. Next to it the audio input. Connect this to the audio line-output of your PC with a standard stereo cable. Fully right is the connector for the headphones or audio amplifier if you use loudspeakers.




The "ButtonBox" has 3 Led's and 3 buttons. The functions of the Led's and buttons depend on the application.

Also a PC or Laptop with software is required. The software consists of a .EXE file, 1 or more language files, and a file with the standard human hearing threshold. The program automatically generates a Init.INI file in which most of the settings are retained for the next time the program is used.
You also need the Visual Basic 6 Run Time Environment and software which emulates serial ports through USB.
A good quality headphone, a very quit room en some patience make things complete.

Installation
The PC-software does not need to be installed. Copy the .EXE file to a suitable directory, e.g. C:\Program Files\TestYouEars\ together with languagefiles and the file with the standard human hearing threshold. You need to have the Visual Basic Run-time environment installed. If not you will get an message like this if you try to run the software:



In that case you must install the VB6 run-time environment. You can download it for free. Follow the installation instructions.

USB-COM port drivers.
The TyE- system uses a virtual COM-port through USB. That means that the program talks to a COM port (serial port) which is actually implemented as a USB connection. The Attenuator Unit translates USB back to serial. To let things work you must have a virtual USB-COM-port driver installed on the PC. There can be found several on the Internet but this one has been tested by the author and works fine. Download the .ZIP-file, unzip it an install. For other operating systems refer to the FTDI website.
Use USBview to check your USB configuration.

Sound device
Basically any soundcard or external sound device can be used.  Connect the Attenuator Unit to the line-output or the headphones output. Do not connect it to an output intended to directly drive loudspeakers (so with a substantial power output)
Disable all whistles and bells from your sound driver software. No (pseudo) multichannel, Bass-Boost, Echo or Surround effects. Only plain left-right stereo is suitable.
Adjust the volume setting to maximum and disable all other programs and services which (possibly) use the sound device.

Headphones
Most of the experiments require a good quality headphones. Some experiments can also be done using a stereo amplifier and (hifi) loudspeakers. Later more about that. The ideal headphones for audiometry is a closed type that covers the ear completely. Closed to suppress noise from the environment as much as possible and covering the ear for a reliable acoustical contact. Unfortunately good quality closed phones are mainly produced for the professional audiometrist's market and likely carry a professional price tag. I have not investigated that.
A good alternative is a high-quality open headphones from the sector Hifi, or if you like, High-end-Hifi. Have a look at Sennheisser or AKG what they have in the pricelist. Count on € 70+
I'd like to advise against the use of earplugs-type phones. Th sound quality is very dependent on how well they are plugged in.
When selecting a headphones for these tests look at the documentation and check it for specifications of the sound level it produces, preferably as a graph giving sound level as function of the frequency. If no graph is given there should be at least a number telling the amount of dB's sound level produced with 1 Volt input signal. See the chapter about calibration.

Starting the program
Before starting the PC-program the Attenuator Unit must have been connected to a USB port and the computur must have recognised the device as a COM-port. You can see that in the Device Manager (Start, Settings, Configuration screen, System, tab Hardware, Device Manager)
You will also see which Commport number the device is assigned. Often this assignment is beyond your control and it may change if you move to another USB-port.
 


Click on "TestYourEars.EXE", or make a shortcut to it on your desktop.
You will see the system window.



Select a language file. The new language will be visible immediately. Settings which are not saved in the initialisation file will get lost (but there ar not many of them)
Select the Commport. You must really click in the digit field to confirm the port number. If the port does not exist you will see a message and you can select another. The program does not detect if the Attenuator Unit is connected to that port. If another device is connected it will be accepted for the moment. You will see that in the next window.
Mark the checkbox if you want to see the Attenuator Panel in the future. In most cases it is not required.
Mark the radio button if you want to use a fixed value for the Headphones sensitivity or if you have a calibration file. (See the chapter about Calibration)
If you have a calibration file select it with the button "Select file" Otherwise enter the calibration factor.  If you do not know that use 90 dB, it will not be far off.
In all cases it is required to calibrate the output level of the sound device. Click on the the button "Calibrate 1 Volt RMS". The procedure takes a few seconds. After that you will see a value in the field "Cal Units". Expect a value between roughly 10000 and 30000. There will be a message if the calibration fails.
Then select the type of test you want to do:
You will also see the Attenuator Control Panel



If the black fields turn white and the box "Peak Value" shows a number the communication with the Attenuator Unit works correctly. If you now press the buttons the respective fields will turn green.
This window is not used in most test so you may shut it down. 
Calibration
There are two things that need calibration, at least for the Hearing Threshold test: The output level of the sound card/device and the sensitivity of the headphones used.
For the output level of the sound card there is an automatic calibration procedure, The soundcard produces a tone of 3000 Hz and a certain amplitude for 1 second. The peak-to-peak level is measured by the A/D converter in the Attenuator Unit and with that value a calculation is done to find which numbers are required to have 1 Volt RMS output level.
The calibration of the headphones can be done in two ways. A single number telling how many dB's sound level are produced for 1 Volt signal. This number can be found in the documentation of the better headphones. It is often around 90 dB for 1 Volt. This way of calibration does not include the frequency dependency of the headphones. You must trust the "flatness" of its frequency characteristic.

Sometimes the calibration is given as so many dB's per milliWATT. In that case you have to do some calculations to find how much that is for 1 millVOLT.
Given the impedance of the headphones R in Ohm, 1 milliWatt equals U = squareroot ( 0.001 * R) in Volts. Then calculate the difference in dB's.
For example: Your 600 Ohm headphones gives 90 dB for 1 milliWatt. For 1 milliWatt you need sqrt(0.001*600) = 0.77 Volts.
0.77 Volts is 20 * log10 (0.77) = -2.2 dB less than 1 Volt, at which the program expects the calibration value. So subtract 2.2 from the value in your datasheet and enter that into the program.
  
It is better if you can find a calibration graph giving the sound level as a function of the frequency at a constant input signal. Such graphs probably are only available for headphones meant for serious hearing measurements and having the appropriate price tag.

Syntax of the Calibration File
The Headphones Calibration file must have the following syntax:
Why a separate box for the Led's and Buttons?
The connection between the PC and the Attenuator Unit is USB. The maximal length of a USB cable is 5 meter. That may be to short to take place in a very silent room (maybe a clothing cabinet) while the PC must be somewhere else. With a separate box for the buttons and Led's the cable can be 10s of meters long. Also the cable for the headphones can easily be extended.
If you use a laptop which makes much less noise than a PC, 5 meter USB cable may be sufficient and you can mount the buttons and leds in the same box as the Attenuator.
Error Messages