Newsletter: GL Announces Oscilloscope & Power Spectral for T1 E1 Audio Applications
Oscilloscope and Power Spectral visuals of analog signals within timeslots is a great way to gain an intuitive understanding of the signals being carried by the timeslots. These features have been standard with GL's T1 E1 platforms for 8 kHz, 8 bit, ulaw and Alaw encoded signals. We have enhanced the features to include higher sampling rates and wider codeword lengths.
This application can be used to visually assess activities on the channel such as noise, tone, speech, etc. The PCM codes (amplitude of the incoming signal) of selected timeslot(s) are displayed in real time graph as a function of time. Timeslot selection and time base can be changed either to view different timeslots or modify the duration of the display. The time base can be adjusted from approximately 0.005 sec full scale to 1.000 sec full scale. The data may be displayed for all signaling formats – Alaw, ulaw, pcm16, pcm13, pcm14, pcm8, and different byte orders INTEL (Little Endian), and MOTOROLA (Big Endian).
The data received on a specified timeslot can be viewed in the spectral domain (spectral amplitude Vs frequency). A Fast Fourier Transform (FFT) is applied to successive sample sets of the incoming data and displayed graphically. Available option to adjust the frequency resolution based on the FFT length is (from 32 points to 8192 points). The data can be smoothed to lessen the effects of truncation by applying Hamming, Hanning, Harris, Blackman, Triangular, or Rectangular filter windows.
In addition to power spectrum display of the incoming signal, the following computations are provided:
- Signal-to-noise ratio for the highest single frequency tone. The noise band can be adjusted to any range within the voice band.
- Total noise power
- Tone power
- Tone frequency
- Total power
The enhancements introduced to Oscilloscope and Power Spectral Display applications include options for displaying all signaling formats – A-Law, Mu-Law, PCM 16 bit, PCM 13 bit, PCM 14 bit, PCM 8 bit and different byte order for INTEL (Little Endian) and MOTOROLA (Big Endian) 16 bit signals sampled at 16 KHz can also be displayed. The computations such as S/N ratio, frequency and different power values corresponding to signals of different formats have also been updated.
Display Control: The graphical display can be magnified and moved by changing the time-base scale depending on the maximum and minimum limits. Further the window can be moved and resized as any other standard window.
Time Base option (Oscilloscope): It helps inselecting the duration of the time displayed. A minimum value of 0.005 sec to a max of 1.000 sec is possible. User can use the spin control to increase or decrease the time span or key in the desired time directly.
Samples (Spectral Display): The sample size upon which the FFT is computed can be adjusted from 32 samples to 8192 samples. The rendering improves in accuracy as the sample size is increased at the expense of losing responsiveness to rapidly changing signals.
FFT Window (Spectral Display): The following smoothing filters are provided: Blackman, Hamming, Hanning, Harris, Rectangular, and Triangular.
Decode Options: This option is available on both Oscilloscope and Spectral Display and provides options for usersto select Data Formats, Sample Rates, and Byte Orders.
- A-LAW: Default signal compression encoding on a DS0 / E1 (North America and Japan)
- Mu-LAW: Default signal compression encoding on a DS0 / T1 (North America and Japan)
- PCM16: For 16-bit 8KHz signals, two consecutive timeslots are used. The byte order, in which the two bytes of 16-bit data, is determined by the selection of INTEL or MOTOROLA byte order options. Similarly, for 16-bit linear, and 16 KHz signals, four consecutive timeslots are used. The lower-numbered timeslot pair carries the earlier 16-bit sample point in time, while the higher-numbered timeslot pair carries the later 16-bit sample point in time. The byte order is determined by the selection of INTEL or MOTOROLA options. The four timeslots, when used in this fashion, make up a four-byte hyper-channel.
- PCM13: Displays 13 bit data on two selected timeslots for 8KHz sample rate. Byte order is determined by the selection of INTEL or MOTOROLA options
- PCM14: Displays 14 bit data on two selected timeslots for 8KHz sample rate. Byte order is determined by the selection of INTEL or MOTOROLA options
Sample Rate: Sample rate option is available only for PCM16 data format. 8KHz and 16KHz sample rate options are available.
Byte Order: Provides INTEL or MOTOROLA byte order options
- INTEL (Little Endian): The lower-numbered timeslot carries the least-significant byte (LSB), while the higher-numbered timeslot carries the most-significant byte (MSB)
- MOTOROLA (Big Endian): The lower-numbered timeslot carries most-significant byte (MSB), while the higher-numbered timeslot carries the least-significant byte (LSB)
Options menu drop-down (Power-Spectral)
- Normal Display:
Selecting this option causes the frequency spectrum of the incoming signal to be repeatedly calculated, and displays the calculated spectrum by updating.
- Averaging Display:
Once a value is specified, the display is averaged over time in accordance with the parameters provided.
- Peak Hold Display:
Selecting this option will retain the max peak value of the samples plotted
- Noise Band:
Noise band is defined as the range of frequencies over which the power is calculated to determine noise power and the signal-to-noise ratio. The default frequency range is 300 Hz to 3400 Hz for 8KHz-sampled signals, and 300 – 7400 Hz for 16 KHz sampled signals.