Real Time

Generating FM Stereo Signals

The following example shows you how to generate FM\Stereo signals with different parameter settings in the Signal Studio software and understand their differences.

1. Generating signal 1, with the carrier parameter settings listed below.

   • Set the RDS to Off, Pilot to Off

   • Set the Audio Source Pattern to L = R

   • Set the Audio Source to Tone(s), and Left Tone(s) to 1.000 kHz 1.000 V.

   The waveform spectrum of Signal 1 is as follows:

   

2. Generating signal 2, with the carrier parameter settings listed below.

   The waveform spectrum of Signal 2 is shown below: 

   • Set Pilot to On

   • Set Normalized to True

   • The other settings remain the same with Signal 1 based on Configuration

   :

   Notice that a FM signal with pilot(19KHz) has been generated.

3. Generating signal 3, with the carrier parameter settings listed below.

   • Set Pre-emphasis to 50us

   • Set Normalized to True

   • Set the Audio Source Pattern to L = R

   • Set the Audio Source to Tone(s), and Left Tone(s) to 1.000 kHz 1.000 V.

   The waveform spectrum of Signal 3 is shown below: 

   

   Comparing signal 2 and 3, it could be derived that when Normalized is True, for single tone, Pre-emphasis has no effect.

   For multiple tones signal, Pre-emphasis will change the relative relationship between multiple tones.

4. Generating signals with the carrier parameter settings listed below. Change Normalized at 15KHz from False to True to compare the results.  

   • Set Normalized to False

   • Set Pre-emphasis to 50us

   • Set the Audio Source Pattern to L = R

   • Set the Audio Source to Tone(s), and Left Tone(s) to 1.000 kHz 1.000 V.

   The audio signal will pass a filter like shown in the figure below.

   

   Notice that there is a warning message shown as follows:

   

   In this case, please reset FM Deviation or Oversampling ratio.

   The waveform spectrum when Normalized at 15KHz is false:

   

   Set Normalized at 15KHz to True:

   The Pre-emphasis gain is 0 dB at 15 kHz. That means the values of y-Axis in the figure will be normalized by 13.66dB.

   This case is commonly used because the input range of VCO is limited.