- Signal generator: sine, rectangle, saw tooth, triangle, frequency sweeps, white noise
- Adjustable quantization of the signals
- Output and input signals: Time scope and FFT spectrum
- SNR, THD+N, gain measurements
- Data logger which creates CSV-files
- Adjustable digital input filter
- Based on: GNU Radio Companion v3.8.5.0-5-g982205bd and Python 3.6.9
- Black-box testing via the PC's sound card:
Development of an Application to Measure the Quality of Audio Devices using GNU Radio by Bennet L. Ladage
This thesis represents a system concept which determines quality indicators of audio devices. It is implemented by GNU Radio, but the concept is described in a way that other software and hardware can realize this system, too.
GNU Radio is chosen as the development environment because of its availability for all main operating systems (i.e., Windows, Linux, and Mac) and due to its open-source license. This software has access to the sound card of the personal computer which is used as an input/output interface for real world signals. Thus, it transfers the PC into a measuring instrument. The second main topic is hence whether the quality of a common sound card is sufficient that the PC is suitable to measure audio devices.
The considered quality indicators are the transfer function, the signal-to-noise ratio (SNR), the total harmonic distortion (THD), the gain and the linear dynamic range (LDR) of audio equipment. If we measure an external audio device, we connect the input of the device under test (DUT) to the sound card’s output, and the DUT’s output is wired to the sound card’s input. This approach is a black-box testing method. For example, equipment like amplifiers, equalizers, mixing consoles, filters, crossover networks, and analog-to-digital (A/D) or digital-to- analog (D/A) converters can be inspected. However, the following test concepts are not adequate for the perceived audio quality of devices which uses low bit rate coding schemes. In addition, the system has a signal generator, a data logger for the quality indicators, an adjustable digital input filter, and a time domain and frequency domain display of the output and input signals.