Stefan Antoszko’s Pink Noise Generator Packs a TI MSP430 and “a Handful of Resistors and Capacitors”

Laptop engineering scholar and digital audio hobbyist Stefan Antoszko has constructed a “pink noise” generator, utilizing a Texas Devices MSP430G2231 microcontroller as a white noise supply and constructing a three-stage filter to attain the specified pink output.

“I used an MCU [Microcontroller Unit] as a white noise supply utilizing a 32-bit Linear Suggestions Shift Register (LFSR),” I handed it right into a three-stage high-shelf filter with offset frequencies to approximate a -3dB slope which is attribute of pink noise. My essential aim from this undertaking was to learn the way the values for [others’] shelf filters have been chosen so I made a decision to derive the equations for them by hand.”

To start out, Antoszko needed to get the TI MSP430 to generate white noise — selecting to make use of a linear suggestions shift register, through which a mix of upper bits are XORed collectively after which pushed to the entrance of the register. “For the reason that MSP430 is a 16-bit MCU, initially I attempted the 15-bit loop the place you XOR the primary and fifteenth bit and push that to the entrance,” Antoszko notes. “Nevertheless, this had a very quick cycle size and I may clearly hear the sequence repeating.”

Selecting a 32-bit variant with two 16-bit registers, Antoszko had an appropriate supply of white noise — however desired pink noise, often known as fractional noise and likened to the sound of a waterfall. To get that required filtering the microcontroller’s output, utilizing “a handful of resistors and capacitors.”

For the expertise, Antoszko calculated what every stage required by hand — taking into consideration how every prior stage has already affected the sign — and got here up with a three-stage filter utilizing 5 resistors and 5 capacitors.

“[The MSP430] is nicely fitted to this software as a result of I solely want one shift register, one output pin, and a 1MHz clock is greater than adequate,” Antoszko concludes. “Moreover, it operates at a low Vcc voltage [of] <3.3V which is useful if I need plug the ultimate sign proper into Line In.”

The total undertaking write-up is on the market on Antoszko’s Hackaday.io web page.