Summary of I2S USB MICROPHONE USING STM32 AND MEMS MICROPHONE
This article describes building an I²S USB microphone to fix audio frequency mismatches in Citrix-hosted virtual desktops. Andy Brown explored two design approaches: a hybrid analog-digital circuit using an analog MEMS microphone and ADC, and a fully digital method utilizing a digital MEMS microphone for direct signal processing. The all-digital approach is noted as more straightforward compared to the analog-dependent first method.
Parts used in the I²S USB Microphone Project:
- Analog MEMS microphone
- Amplifier and conditioning circuit
- Analog-to-Digital Converter (ADC)
- Digital MEMS microphone
- USB audio output interface
- STM32 microcontroller
Virtual desktops are used extensively in the IT sector currently due to the COVID-19 pandemic. This set-up allows the employees to work remotely and is convenient. Virtual desktops are preconfigured images of operating systems and applications in which the desktop environment is separated from the physical device used to access it. Users can access their virtual desktops remotely over a network. Andy Brown found a problem while joining meetings in his company’s Citrix-hosted virtual desktop, he observed that the video was fine but the audio frequency on the VDI was mismatched to the actual frequency on the physical device. He described that he sounded like Mickey Mouse on Helium.
The solution to this mismatch in frequency is changing the frequency on the VDI that requires administrator-level access. Andy tried installing a microphone app on his phone that acts as a USB microphone when connected to a computer. But he needed a dedicated USB microphone and so he decided to build an I²S USB microphone. He came up with two possible implementation approaches. The first approach is partly analog and partly digital microphone circuits. The second method is to design with all digital components and techniques.
First Method: Partly Analog USB Microphone
In this method, an analog MEMS microphone is used as a transducer. The signal from the microphone will be then amplified and conditioned. Next, the ADC will convert them into digital signals. This stage is necessary for performing digital signal processing. In analog signal processing, a high level of accuracy can’t be achieved as the accuracy depends on the tolerances circuit components. After processing, the signal is ready to go to the USB audio output.
Second Method: All-Digital USB Microphone
In this approach, a digital MEMS microphone is used. The microphone produces signals that can be directly processed digitally. Thus, digital signal processing is performed directly on the microphone signals and after processing, the signal is provided at the USB audio output. It can be observed that this looks like a straightforward method as compared to the first approach.
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- What problem did Andy Brown encounter with his virtual desktop?
He observed that the audio frequency on the VDI was mismatched to the physical device, making him sound like Mickey Mouse on Helium. - How can the audio frequency mismatch in a VDI be resolved?
The solution involves changing the frequency on the VDI, which requires administrator-level access. - Why did Andy decide to build an I²S USB microphone instead of buying one?
He needed a dedicated USB microphone because installing a phone app acting as a USB mic was not sufficient for his needs. - What are the two implementation approaches described for the microphone project?
The first is a partly analog and partly digital circuit, while the second uses all digital components and techniques. - Which method uses an analog MEMS microphone as a transducer?
The first method, known as the Partly Analog USB Microphone approach, uses an analog MEMS microphone. - Why is high accuracy difficult to achieve in analog signal processing?
Accuracy depends on the tolerances of circuit components used in the analog stage. - How does the all-digital approach process signals differently?
A digital MEMS microphone produces signals that can be directly processed digitally without needing an ADC stage first. - Which approach is considered more straightforward according to the text?
The all-digital method using a digital MEMS microphone is observed to be straightforward compared to the first approach.
