Tweet
The Diamond Cut Spectrum Analyzers
There are two versions of the Diamond Cut Spectrum Analyzer available in the version 10 product family. The DCArt10 version provides a Standard Precision Spectrum Analyzer providing excellent resolution especially at the low frequency end of the audio spectrum. The DC Forensics version provides a High Precision Spectrum Analyzer with higher frequency resolution over the entire audio frequency spectrum coupled with a display which can zoom in on a specific frequency range via a start and stop frequency feature. The High Precision Spectrum Analyzer also offers the user the option of octave based 10 and 30 band displays for use in acoustical measurement situations.
Spectrum Analyzer – Standard Precision (DCArt10)
The Spectrum Analyzer command in DCArt10 brings up the floating and user sizable Standard Precision Spectrum Analyzer. The Spectrum Analyzer is capable of resolving frequency increments as small as 0.02 Hz on 44.1 KHz sample rate files when it is set appropriately. This Analyzer can be used with any of the filters or effects. It is connected to the output of the filter or effect, so that you can see, in the frequency domain, how you have affected the file. If you want to compare the output of the filter or effect to the input, use the Bypass function on the filter or effect window. Since the Diamond Cut Spectrum Analyzer utilizes constant Hertz per frequency band, it will display white noise as a flat, horizontal line. This is unlike octave weighted real time audio analyzers in which white noise produces a diagonal, positive sloped line, and pink noise produces a flat horizontal line. Conversely, pink noise displayed on the Diamond Cut Spectrum Analyzer will be displayed as a negative sloped diagonal line. Normally, the Spectrum Analyzer displays the algebraic sum of the left and right channels. The Dual Waveform Display option will provide discrete displays for each channel. Keep in mind that the use of the Spectrum Analyzer will slow your system down slightly. Therefore, when you are done using it, shut it down.
The Standard Precision Spectrum Analyzer
The following displays are provided on the Spectrum Analyzer:
The following controls are provided:
Spectrum Analyzer Resolution Chart
Note 1: Because the FFT creates solutions in both the real and imaginary planes, the actual number of frequency bands created is the FFT Size/2.
Note 2: NA = Not Applicable
The following chart shows the performance of several of the provided Window functions. Others are provided with the software for completeness.
Note:Hanning is the recommended default window to use for general applications.
This selector box (Show THD) found under the Option Menu converts the Spectrum Analyzer into a high performance Harmonic Distortion Analyzer when enabled. It measures % THD (percent Total Harmonic Distortion). A pure Sine wave obtained from either a very high quality external signal generator or the "Make Waves" generator must be used as the stimulus for an external device under test (DUT) or algorithm under test. The THD meter measures the fundamental signal component separating it from the rest of the total harmonic signals presented to the system. It also "notches" out the fundamental and sums the remaining harmonics. Then it takes the ratio of the fundamental signal component to the square root of the sums of the squares of the measured harmonics and expresses it as a percentage on the digital readout. Even and Odd order distortion components are produced by transfer function non-linearity, both of which are measured by this system. Even-multiple harmonic products are dominantly due to transfer function asymmetry.
Note 1: The Show Peak checkbox must be checked before enabling the THD display.
Note 2: When not using the Distortion Analyzer, turn it off to minimize CPU utilization.
There are two versions of the Diamond Cut Spectrum Analyzer available in the version 10 product family. The DCArt10 version provides a Standard Precision Spectrum Analyzer providing excellent resolution especially at the low frequency end of the audio spectrum. The DC Forensics version provides a High Precision Spectrum Analyzer with higher frequency resolution over the entire audio frequency spectrum coupled with a display which can zoom in on a specific frequency range via a start and stop frequency feature. The High Precision Spectrum Analyzer also offers the user the option of octave based 10 and 30 band displays for use in acoustical measurement situations.
Spectrum Analyzer – Standard Precision (DCArt10)
The Spectrum Analyzer command in DCArt10 brings up the floating and user sizable Standard Precision Spectrum Analyzer. The Spectrum Analyzer is capable of resolving frequency increments as small as 0.02 Hz on 44.1 KHz sample rate files when it is set appropriately. This Analyzer can be used with any of the filters or effects. It is connected to the output of the filter or effect, so that you can see, in the frequency domain, how you have affected the file. If you want to compare the output of the filter or effect to the input, use the Bypass function on the filter or effect window. Since the Diamond Cut Spectrum Analyzer utilizes constant Hertz per frequency band, it will display white noise as a flat, horizontal line. This is unlike octave weighted real time audio analyzers in which white noise produces a diagonal, positive sloped line, and pink noise produces a flat horizontal line. Conversely, pink noise displayed on the Diamond Cut Spectrum Analyzer will be displayed as a negative sloped diagonal line. Normally, the Spectrum Analyzer displays the algebraic sum of the left and right channels. The Dual Waveform Display option will provide discrete displays for each channel. Keep in mind that the use of the Spectrum Analyzer will slow your system down slightly. Therefore, when you are done using it, shut it down.
The Standard Precision Spectrum Analyzer
The following displays are provided on the Spectrum Analyzer:
- Frequency vs. Amplitude Graph: The vertical axis indicates 0 dB at the top and ranges down to -100 dB at the bottom by default. The amplitude range can be changed via the Amp Range control. The horizontal axis indicates frequencies from 10 Hz (left) to a little over 20 kHz (right).
- Two digital readouts indicate the frequency and amplitude of signals feeding the Spectrum Analyzer. One signal is the peak value and the other is user defined.
The following controls are provided:
- Display Mode:
- Fast: Shows the spectrum in almost real time.
- Slow: Shows the spectrum with slower ballistics.
- Averaging: On/Off: This allows the system to provide you with the average signal spectrum rather than in “Fast” real time display. The averaging time interval will be as long as the analyzer is left in operation or until the “Clear” button is activated. The looped play function is sometimes useful in conjunction with the Averaging function.
- Dual Waveform Display: This checkbox allows you to view both the left and right channels simultaneously on the Spectrum Analyzer display provided that you are working with a stereo .wav file. The right channel information will be displayed in red while the left channel is displayed in yellow. If you operate this feature with a monophonic .wav file input, the display will be shown in yellow.
- FFT Size: 11 selection alternatives (64, 128, 256, 512, 1,024, 2,048, 4,096, 8,192, 16,384, 32,768, & 65,536). This selection determines the frequency resolution of the spectrum analyzer. The higher the number selected, the better the frequency resolution of the display. The Forensics version extends the FFT Size range up to 131,072.
- Range: (Amp Range) The Amplitude Range control scales the vertical axis to 150 dB, 100 dB, 50 dB, or 20 dB for full scale deflection. This feature along with the offset control allows you to hone in on a particular signal.
- Hold Button: This is a "toggle" function and will allow you to freeze or un-freeze the spectral display update.
- Clear Button: This clears the display. It is especially useful when using averaging mode so that you can clear the display after a long averaging interval, allowing you to move onto a new area of the Waveform to be averaged. Clearing the display will re-initiate the averaging process as well as clearing the display.
- Show Peak Button: This feature will automatically find the peak amplitude signal and display its Frequency and Relative Amplitude value in the upper right hand corner of the Spectrum Display screen. The marker and display for this feature are red in color.
- User Controlled Marker: You can place a marker anywhere you want on the spectral display by clicking the left mouse button on the signal that you are interested in measuring. To accomplish this, merely point the mouse cursor to the peak of interest and click the left mouse button. A magenta colored marker line will appear at that location and a yellow digital display of the frequency and relative amplitude of the signal that you pointed to will appear in the upper left hand corner of the spectral display. To read another value, merely click the mouse again after pointing to a new spectral line. The marker and the display will then be updated.
- Frequency Resolution: (Standard Resolution version – non-Forensics.) The Spectrum Analyzer has the ability to display frequencies with the following values of resolution as indicated on the chart below. Note the interaction between the FFT Size selected and the available Resolution in Hz that are available: “OK” indicates available ranges. “NA” indicates Not Available resolution values by Frequency Band. It is very important to note that small values of FFT Size produce poor values of Resolution, but the response will be very fast. Conversely, large values of FFT Size produce good values of Resolution, but the response will be very slow. This latency time (or display refresh / update) is a function of the Spectrum Analyzer frequency resolution setting. The latency expressed in Seconds, is displayed in the right-hand column for each value of resolution.
Spectrum Analyzer Resolution Chart
| 0.02 | 0.04 | 0.08 | 0.17 | 0.34 | 0.68 | 1.35 | 2.96 | 5.38 | 10.77 | 21.53 | 43.07 | 86.13 | 172.27 | 344.53 | 689.06 | Res. Hz | FFT Size | |
| NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | 64 | ||
| NA | NA | NA | NA | NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | 128 | ||
| NA | NA | NA | NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | 256 | ||
| NA | NA | NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | 512 | ||
| NA | NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | 1,024 | ||
| NA | NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | 2,048 | ||
| NA | NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | NA | 4,096 | ||
| NA | NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | NA | NA | 8.192 | ||
| NA | NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | NA | NA | NA | 16,384 | ||
| NA | OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | NA | NA | NA | NA | 32,768 | ||
| OK | OK | OK | OK | OK | OK | NA | NA | NA | NA | NA | NA | NA | NA | NA | NA | 65,536 | ||
| 64 | 32 | 16 | 8.0 | 4.0 | 2.0 | 1.0 | .5 | .250 | .125 | .0625 | .0312 | .0156 | .0078 | .0039 | .002 | (In Secs) | Latency |
Note 2: NA = Not Applicable
- Offset Slider Control: This allows you to move the centering of the spectral display up or down. It is of particular value when the "Range" control is set to a high sensitivity value such as 50 dB or 20 dB, and the signal appears to be off of the screen. By using the Range control and the "Offset Slider" control, you can zoom-in on a signal of interest.
- Window Selection: Seven window selections are provided so that you can establish the appropriate tradeoff between Stop Band attenuation and Lobe Width.
- Blackman
- Hanning
- Hamming
- Rectangular
- Kaiser 10
- Kaiser 20
- Kaiser-Bessel
- Triangular
- Bessel
- Welsh
The following chart shows the performance of several of the provided Window functions. Others are provided with the software for completeness.
| Window Name | Side-Lobe Peak Amplitude in dB | Main Lobe Band-pass Width | Minimum Stop-Band Attenuation in dB |
| Blackman | -57 | 12 pi / N | -74 |
| Hanning | -31 | 8 pi / N | -44 |
| Hamming | -43 | 8 pi / N | -53 |
| Rectangular | -13 | 4 pi / N | -21 |
| Window Name | Characteristics | Application |
| Blackman | Exhibits the best amplitude resolution and accuracy, but has the poorest frequency resolution | Very Good for measuring single frequency signals in order to look at its higher order products. |
| Hanning | This exhibits fair frequency resolution but poorer amplitude accuracy compared to the Rectangular Window | Good for measuring Narrow Band random Noise, measuring Periodic Signals and for measuring transient bursts wherein the signal levels prior to and just after the event are much different in amplitude. |
| Hamming | This window is very similar to Hanning, however it exhibits slightly better frequency resolution and accuracy compared to Hanning | Same Applications as Hanning. |
| Rectangular | Exhibits the best frequency resolution, but has the poorest amplitude resolution and accuracy. In essence, Rectangular is not a window, per se, at all. | Good for measuring sine waves that have similar amplitudes and whose frequencies are loose, for measuring broad band noise with slowly varying frequency spectrum and for measuring Transient bursts wherein the signal levels before and after the key event are similar in amplitude |
- Display Type (Option Menu): Choose between “Line” or “Bar” (Graph) modes. Default is “Line”. When “Bar” is activated, the display reverts to that mode.
- Display Size (Option Menu): The overall physical dimensions of the Spectrum Analyzer are user sizable. Simply use your mouse to drag its horizontal and vertical margins to create a display size to your liking.
- Show Peak (Option Menu): Automatically finds and displays the largest signal spike on the Spectrum Analyzer display.
- Dual Waveform Display (Option Menu): Reverts to stereo display mode showing each channel as separate traces on the graph. The Right Channel is shown in Red while the Left is shown in Yellow.
- Show Power Spectrum (Option Menu): This option displays the power x time product (energy) of the presented signal at various frequencies.
This selector box (Show THD) found under the Option Menu converts the Spectrum Analyzer into a high performance Harmonic Distortion Analyzer when enabled. It measures % THD (percent Total Harmonic Distortion). A pure Sine wave obtained from either a very high quality external signal generator or the "Make Waves" generator must be used as the stimulus for an external device under test (DUT) or algorithm under test. The THD meter measures the fundamental signal component separating it from the rest of the total harmonic signals presented to the system. It also "notches" out the fundamental and sums the remaining harmonics. Then it takes the ratio of the fundamental signal component to the square root of the sums of the squares of the measured harmonics and expresses it as a percentage on the digital readout. Even and Odd order distortion components are produced by transfer function non-linearity, both of which are measured by this system. Even-multiple harmonic products are dominantly due to transfer function asymmetry.
Note 1: The Show Peak checkbox must be checked before enabling the THD display.
Note 2: When not using the Distortion Analyzer, turn it off to minimize CPU utilization.