Wolfson - voice record volume too low using DMIC

Question

Hi,

I just got my wolfson card running on a raspberry pi today, I'm able to record using the built in microphone, but the volume is really low, or I need to be really close to the board. I have no idea what the commands in the Record_from_DMIC.sh really mean, I changed the volume values to a higher value but they don't seem to make any difference.

What I would like to do is, be about 8 feet away from the board and have it record my voice (so I can integrate it in my current project Go Cortex - using voice recognition and an ultrasonic sensor )

Any help would be greatly appreciated.

I'm using the os I downloaded from the element14 site. Let me know what other information you may need.

Thanks

Diego

Former Member · Accepted Answer

Hi! Yes, the use case scripts are a bit cryptic, aren't they? As you have probably seen, there are two volume controls for each channel involved when recording from the DMICs. IN2L Digital Volume and IN2R Digital Volume control the output levels of the DMICs. Valid values for these are 0 - 191. AIF1TX1 Input 1 Volume and AIF1TX2 Input 1 Volume control the levels of the signals sent to the RPi. Valid values are 0 - 48. So, if you want to really max it out, set them to 191 and 48 respectively. I have observed DC offset when recording the DMICs and a bit of hiss creeps in when you crank the levels up. I've made my own script that sends the sound from the DMICs through high-pass and low-pass filters to alleviate that: #!/bin/bash
# Record from on-board DMICs to RPi.
# First, route signal from DMICs through High-Pass Filter to get rid of DC offset.
# Then, route output from High-Pass filter through Low-Pass Filter to get rid of high-freq noise and hiss.
#
# IN2 --> HPF --> LPF --> AIF1TX

# Set default levels. May be overridden by environment variables.
DMIC_OUTPUT_LEVEL=128 # Output level from DMICs. Valid values: 0 - 191
RECORDING_LEVEL=32 # Level of signal sent to the RPi. Valid values: 0 - 48

# Check for environment variables.
[ ! -z "$DL" ] && DMIC_OUTPUT_LEVEL=$DL
[ ! -z "$RL" ] && RECORDING_LEVEL=$RL

# DMIC output level. Valid values 0 - 191
amixer -Dhw:0 cset name='IN2L Digital Volume' ${DMIC_OUTPUT_LEVEL}
amixer -Dhw:0 cset name='IN2R Digital Volume' ${DMIC_OUTPUT_LEVEL}

# DMICs are incorrectly labeled on the board.
# DMICL is actually the right channel and vice versa, so we swap them here.
# i.e. IN2R --> LHPF1
# IN2L --> LHPF2
# Route DMICs (IN2) to LHPF{1,2} - High-pass filter to get rid of DC offset.
amixer -q -Dhw:0 cset name='LHPF1 Input 1' IN2R
amixer -q -Dhw:0 cset name='LHPF2 Input 1' IN2L
amixer -q -Dhw:0 cset name='LHPF1 Mode' High-pass
amixer -q -Dhw:0 cset name='LHPF2 Mode' High-pass

# Route output of LPHF{1,2} to LHPF{3,4}. Low-pass filter to get rid of hiss.
amixer -q -Dhw:0 cset name='LHPF3 Input 1' LHPF1
amixer -q -Dhw:0 cset name='LHPF4 Input 1' LHPF2
amixer -q -Dhw:0 cset name='LHPF3 Mode' Low-pass
amixer -q -Dhw:0 cset name='LHPF4 Mode' Low-pass

# Connect outputs of Low-Pass filters to inputs of AIF1 (I2S to RPi)
amixer -q -Dhw:0 cset name='AIF1TX1 Input 1' LHPF3
amixer -q -Dhw:0 cset name='AIF1TX2 Input 1' LHPF4

# Recording level. Valid values 0 - 48
amixer -Dhw:0 cset name='AIF1TX1 Input 1 Volume' ${RECORDING_LEVEL}
amixer -Dhw:0 cset name='AIF1TX2 Input 1 Volume' ${RECORDING_LEVEL}

amixer -q -Dhw:0 cset name='DMIC Switch' on Save the above as Record_from_DMIC_HPF_LPF.sh and make it executable with chmod +x Record_from_DMIC_HPF_LPF.sh In order to save myself from constant editing of the script to set the levels, I've made it so it can take values from two environment variables; DL and RL ( D igital L evel and R ecording L evel). To set max levels, call the script like this: DL=191 RL=48 ./Record_from_DMIC_HPF_LPF.sh Now, experiment with the DL and RL values! -- Ragnar