A system comprising: a wearable member (102, 200, 400, 902) including: an energy transmitter (204, 1004) configured to project energy into tissue of a user; an energy receiver (206, 1006) configured to generate a multichannel signal based on a first received portion of the energy, the first received portion of energy being received through the tissue of the user; a processor; memory storing instructions that, when executed by the processor, cause the processor to: select a first type of respiratory rate classifier or a second type of respiratory rate classifier, wherein the first type of respiratory rate classifier does not require calibration to determine filter parameters, the second type of respiratory rate classifier is a specific classifier which requires calibration to determine filter parameters, the specific classifier depending on information about the user; filter noise from the multichannel signal using the selected respiratory rate classifier; determine a spectrum of the multichannel signal; determine a first respiratory rate from the spectrum of the multichannel signal; obtain a noise reference; obtain one or more second respiratory rates; and determine a third respiratory rate based on the first respiratory rate, the noise reference, and the one or more second respiratory rates; and a communication module configured to provide a message including or being based on the third respiratory rate. a wearable member (102, 200, 400, 902) including: an energy transmitter (204, 1004) configured to project energy into tissue of a user; an energy receiver (206, 1006) configured to generate a multichannel signal based on a first received portion of the energy, the first received portion of energy being received through the tissue of the user; an energy transmitter (204, 1004) configured to project energy into tissue of a user; an energy receiver (206, 1006) configured to generate a multichannel signal based on a first received portion of the energy, the first received portion of energy being received through the tissue of the user; a processor; memory storing instructions that, when executed by the processor, cause the processor to: select a first type of respiratory rate classifier or a second type of respiratory rate classifier, wherein the first type of respiratory rate classifier does not require calibration to determine filter parameters, the second type of respiratory rate classifier is a specific classifier which requires calibration to determine filter parameters, the specific classifier depending on information about the user; filter noise from the multichannel signal using the selected respiratory rate classifier; determine a spectrum of the multichannel signal; determine a first respiratory rate from the spectrum of the multichannel signal; obtain a noise reference; obtain one or more second respiratory rates; and determine a third respiratory rate based on the first respiratory rate, the noise reference, and the one or more second respiratory rates; and select a first type of respiratory rate classifier or a second type of respiratory rate classifier, wherein the first type of respiratory rate classifier does not require calibration to determine filter parameters, the second type of respiratory rate classifier is a specific classifier which requires calibration to determine filter parameters, the specific classifier depending on information about the user; filter noise from the multichannel signal using the selected respiratory rate classifier; determine a spectrum of the multichannel signal; determine a first respiratory rate from the spectrum of the multichannel signal; obtain a noise reference; obtain one or more second respiratory rates; and determine a third respiratory rate based on the first respiratory rate, the noise reference, and the one or more second respiratory rates; and a communication module configured to provide a message including or being based on the third respiratory rate.