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Review by Allan Linton-Smith EVOR04 real-time Audio Spectrum Analyser This device cost $110 on eBay. It incorporates a spectrum analyser, oscilloscope, VU meter and frequency meter plus more. But is it a tool or a toy? A udio analysers are usually a rare breed, and are generally not anywhere near the budget of DIYers. But they are getting cheaper, smaller and better, and this is a great example of such a device! So is it a tool, or just a toy with a colourful screen? We put it to the test and found that it is remarkably accurate and easy to use. This little gadget combines a spectrum analyser, an oscilloscope, a VU meter and a frequency meter. It also has a few extra bells and whistles, such as a goniometer (which generates Lissajous figures on the X/Y oscilloscope setting). The EVOR04 gives you a stereo audio spectrum in real-time via a 31-band FFT analysis (1/3rd octave). This feature was previously only available on very specialised and expensive devices, such as the Keysight 35670A. Using it Connecting up the analyser is very simple. You can feed in audio signals via shielded cable to a set of screw terminals. If you wish, you can wire up a second set of signals; you can then switch between them. It will run from 5-24V DC, again wired to screw terminals. USB power (5V) is suitable. Once it has been wired up and powered on, simply tap the screen to bring up the main menu and select your preferred mode: spectrum, VU, oscilloscope etc. You can check out the instructions on YouTube for more detail, at https:// youtu.be/vQxXD6dpaCo This device is sensitive down to siliconchip.com.au 2.2mV RMS (AC), but should not be fed with more than 2V RMS. That means it will accept some ‘line-level’ signals, but if you’re taking the output from a CD player, DVD player, Blu-ray player or DAC, you might need to add series resistors to attenuate the signals to a safe level, in combination with the device’s internal input impedance. You could also feed in larger amplitude signals, such as the outputs of power amplifiers. In that case, you would need to add resistive dividers with appropriate power ratings and division ratios to both reduce the signals to safe levels, and prevent them from clipping when the EVOR04 samples them. Viewing modes Screens 1-7 show examples of some of the viewing modes. Note that many of these have adjustable parameters. These are, in order: frequency counter, real-time stereo audio spectrum, VU meter (analog-style), VU meter (bargraph style), goniometer, dual spectrum analyser and oscilloscope waterfall. USB interface The module is equipped with a USB communication interface. With the VuRemote Windows software, it is possible to access all configurable options. This software has the following features: Features ● 3.5in colour TFT LCD touchscreen ● runs from 5-24V DC including USB ● seven modes: VU meter, 31-band real-time spectrum analyser, oscilloscope, envelope, goniometer (X/Y plot), VU meter, frequency meter ● two displayed channels, individually selectable from four inputs ● 167 adjustable parameters ● 48 programmable presets ● 127 image slots for background and skins ● 8Hz to 22kHz bandwidth ● USB communication with a PC Specifications ● ● ● ● ● ● ● ● Supply voltage: 4.8-5.2V DC (USB), 4.2-24.2V (PWR) Operating current: 165-180mA <at> 5V; 38-45mA <at> 24V Input signal range: -2.7V DC to +2.7V DC Adjustable 0dB reference: 2.2mV RMS (-53dBv, -50.8dBu) to 2V RMS (+6dBv, +8.2dBu) Noise level: -85dB with respect to 2V RMS Input impedance: 33-38kW Regulated output voltage: 3.3V (3.1-3.4V), max 50mA draw Input signal levels: 0-0.6V (low), 2.2V to V+ (high) Australia’s electronics magazine May 2021  61 1 • • • • adjust effect and input parameters change images store and load presets store and load the configuration to/from a file • backup and restore • take a snapshot of the screen 2 Applications 3 4 5 6 7 Screens 1-7: some of the viewing modes include a frequency counter, real-time stereo audio spectrum, VU meter (analog), VU meter (bargraph), goniometer (an instrument for measuring angles), dual spectrum analyser, and oscilloscope waterfall. Below: the bottom side of the EVOR04 audio analyser, which measures 108 x 84 x 30mm. 62 Silicon Chip Australia’s electronics magazine So, is it a real instrument or just a nice toy to attach to your amplifier or speaker system? The answer will pretty much be determined by your needs. To try to solve this conundrum, we ran the unit through several tests. To measure signal amplitude, you first have to set up the EVOR at 0dBv or 1V RMS, by adjusting the input amplitude for both channels using the attenuators. Once you are confident that 0dBV is exactly 1V RMS, all the subsequent VU measurements you make can be quantified. We found that the results it gave were generally accurate after this calibration. Screen 8 shows the oscilloscope display when applying a 441Hz square wave to the unit’s inputs. This shows minimal overshoot, and it automatically triggered to give a stable trace. Screen 9 shows the unit in frequency counter mode, measuring a 441Hz signal from an accurate Audio Precision generator. It is accurate to 1Hz as long as the resolution is set at 1Hz. This mode can be very useful for tuning instruments using a microphone and amplifier, or you could use it to calibrate other instruments. Screen 10 is a goniometer trace (Lissajous figure / Bowditch curve) created by the oscilloscope mode on the X/Y setting. The horizontal axis is fed by signals from the left channel input, while the right channel input signal feeds the vertical axis. In this case, the signals were oscillators set at 2kHz and 4kHz, respectively. Screen 11 shows an intermodulation distortion (IMD) test signal being applied in oscilloscope mode. This is a combination of 250Hz and 8kHz sinewaves. It is not synchronised, but this signal fools most benchtop scopes! Screen 12 is a spectral analysis of the same IMD signal, and accurately shows the two signals at a 4:1 amplitude. Further testing showed that the unit can measure harmonic distortion down to -85dB or 0.005%, providing the input amplitude is close to the maximum permitted (6dBv). siliconchip.com.au 8 9 10 11 12 13 Screens 8-13: osilloscope with a 441Hz square wave, frequency counter mode, goniometer trace, intermodulation distortion test signal, spectral analysis of the previous distortion test signal, and one of the VU meter displays. Screen 13 shows one of the VU meter displays which, as mentioned earlier, is accurate as long as the input levels are correctly calibrated. Conclusion This is an interesting and accurate analytical tool. It would be handy for anyone who dabbles in audio for checking amplitude, frequency and distortion in amplifiers, preamplifiers and speakers (with a suitable microphone & preamp). It could also be useful for checking or calibrating other audio instruments such as oscillators, oscilloscopes and multimeters. Every audio experimenter should probably have one of these in their kit. It could be mounted in a Jiffy box or similar; consider that the module is ‘bare bones’ and could be damaged if it is placed on a metal surface or obsiliconchip.com.au ject, or a wire or component comes in contact with it. But probably its best use is mounting it in the front panel of an amplifier to provide some interesting displays while using it! In addition to the ‘nuts and bolts’ functions, it has a fun quality and would look really smart integrated with audio equipment. You could then ‘watch’ your music and monitor it for any clipping, amplitude or balance problems. Or you can just look at the pretty display! The EVOR04 can be purchased at: http://sch-remote.com/index.php www.ebay.com/itm/171765947707 And check out these videos: “EVOR Color VU meter, Real Time Analyzer Demo” – https://youtu.be/ vQxXD6dpaCo “Modern HIFI Oscilloscope & Waveform & Spectrometer” – https://youtu. be/CfbP-7xE1Oo SC Australia’s electronics magazine May 2021  63