View Single Post
  #19 (permalink)  
Old 07-08-2005, 8:36 AM
EricCottrell EricCottrell is offline
Member
   
Join Date: Nov 2002
Location: Boston, Ma
Posts: 1,136
Default

Quote:
Originally Posted by nyscan00
Quote:
Originally Posted by 1080iAddict
I finally got my test station to tone out and I knew the tone was coming because the dispatcher reads the box first. I am pretty positive I programmed the 396 correctly with the proper HZ frequencies, duration, gap, etc. - - it was all measured using Adobe Audition software.
Hi can you share how to deturmine and measure a tone recording in HZ? I have Cool Edit and Audacity editing programs but am not sure how to measure the tone in HZ??

Anyone familar with this? :?:

Thanks
Hello,

You can use Audacity directly to figure out the tone frequencies. I use a method of finding frequency by using the period of a cycle of the waveform. Period is converted to frequency by the equation Frequency = 1/Period. With the Audacity audio editor you can find the period by doing a mouse click to put the cursor at a positive zero crossing and, while holding down the mouse button, drag the selection over to the next positive zero crossing. At the bottom are selection time values and the period is the difference time shown in the parentheses. You can use any point of the cycle to the same point in another cycle, but I use the zero crossings to make it easier. I zoom up to display 11 cycles or so, select 10 cycles and then divide the difference time (period) by 10 to get a more accurate count. Another nice feature with Audacity is you can zoom the vertical scale up to see the area around zero. This allows more accurate determination of the zero crossing.

By using the time marks you can measure tone times as well.

I was able to figure out what system my local fire department was using after a few Pages. They are using QuickCall 2. To make things easier I precalculated the periods for the tones in the Groups I am interested in.

I find this method easier than using a frequency counter. It is more direct and eliminates any errors from the frequency counter. You can still get good readings on distorted or noisy waveforms if you use the same point on each cycle to make the measurement. Frequency Counters can have problems if the waveform is not a clean sine wave.

I use Scanner Recorder to record the tones. I recorded using 44.1 16-Bit bit Mono WAV. I figure that using compression may affect frequency accuracy.

73 Eric