RTASC Lite - Real Time Audio System Check Lite

dspconcepts.com
Real-TimeAudioSystemCheckLite
UsingAudioWeaverDesigner
-Version 0.4
v3

WELCOME TO THE NEW SPEED OF SOUNDdspconcepts.com 2
Contents
1. What's, Whys & How's of RTASC!
2. Equipment Needed (HW/SW)
3. Background Info - Microphones
4. Understanding Microphones
5. RTASC Setup
6. Microphone Matching Check
7. Mic Gain / Sensitivity
7. Microphone Isolation Test
8. Microphone Noise Floor
9. Speaker THD
10. Conducted Sound Test
11. Reference Signal to Microphone
Latency Check
12. Basic AEC Check

What's, Whys & How's of RTASC!
• RTASC = Real-Time Audio System Check
• A step-by-step guide for verifying hardware and software functionality of an audio product
• It is specifically targeted at OEMs making voice enabled products having both microphones and
loudspeakers
• The test is aimed at hardware engineers and embedded software engineers. No DSP knowledge
required.
• If your system passes RTASC then the DSP Concepts’ TalkTo voice front end will drop in and run at full
performance
• RTASC can identify multiple issues which are typically found at the start of development
• AudioWeaver Designer Check:-
• Register an account on the DSP Concepts website. The standard evaluation license is free for 30 days.
Purchase the license it to get complete modules.

• AWELib integrated into your product
• Received a customized release on the target platform from DSP Concepts.
• Run the “simple” application inside the AWELib tarball, and pass the “simple” test.
• Run at least a demo or reference design in a DSP Concepts-supported platform, such as TalkTo Sample
App on Raspberry Pi.
• Make sure that your ALSA audio devices are working
• ALSA Device Check
arecord -l
aplay –l
• Record from the microphones. For example:
arecord -D hw:0,3 -f S32_LE -r 16000 -c 16 test_record_mic.wav
• Play the recorded file. For example:
aplay -D hw:0,2 test_record_mic.wav
What's, Whys & How's of RTASC!

Equipment Needed (HW/SW)
• SPL meter
• Recommended: REED Instruments R8080 sound level meter
• Get the link to the device HERE!
• Acoustic putty
• Recommended: Loctite FUN-TAK
• Loudspeaker
• Recommended: Fostex 6301NE
• Loudspeaker stand
• Build your own/ buy a repurposed stand from the link
• Get the link to the product HERE!
• PC
• For AWE Designer and generating tone/noise.
• Sine wave generator
• Use Audacity (Recommended)
• Or use “Simple Tone Generator” (Via Bluetooth)
• Noise generator
• Use Audacity (Recommended)
• Or use “Noisli” (Via Bluetooth)

Part number ST MP34DT01
Sensitivity -26 +/- 3 dB
AOP 120 dBSPL
SNR 63 dB
Block size 768 samples
Sample rate 48 kHz
Input channels 10 Channels
1,3,5,7 Microphones
9,10 Reference
2,4,6,8 Unused
Shape of Mic Array Circular
Distance Between the Microphones 35 mm radius
Microphone Interface (Analog/Digital) Digital PDM MEMS
Example Your Device
Background Info - Microphones
Q) Do you have the
microphone
datasheet? Attach it
to the folder
/RTASC-
Results&Attachmen
ts

Device Check Command arecord -l
aplay -l
Command to record from the microphones. arecord -D hw:0,3 -f S32_LE -r 16000 -c 16
test_record_mic.wav
Command to play the recorded file. aplay -D hw:0,2 test_record_mic.wav
Example Your Device
Background Info - Commands

120 dB Acoustic
overload point
0 dB
94 dB Reference level-26 dB
Digital Level (FS) Acoustic Level (SPL)
Sensitivity
= -26 dB
31 dB Noise floor-89 dB
SNR
= 63 dB
Understanding Microphones
Need Sensitivity and SNR values from your
microphone datasheet
Use dBA for microphone measurements.

RTASC Setup
• Place the DUT on a stand in free field (fewer
reflections than being on a table)
• Place the speaker above the DUT centered over the
microphones
• Height of the stand ~20cms.
• Place an SPL meter near the microphones on the
DUT.
• All the Checks in RTASC should be performed in a
quiet room around 35- 40dBA or lower.
• Click on the icon for the RTASC Videos

• Open the design RTASC-Lite.awd
• Generate a 1 kHz sine tone to play out of an external
speaker.
• Place the speaker cone 20cm above the middle of the
device.
• Calibrate the sine tone to 75 dBA in a quiet room.
• Verify by making sure to place the SPL meter very close
to the device microphones.(Not at the speaker!)
• Check Meter_Mic in designer to see whether the
microphone channels are within +/- 1 dB
• Take a screenshot of Meter_Mic and paste on the
results page.
Example

RTASC-Lite.awd
1) Rt Click  View
Properties
Arguments
numOutChannels. To
change the number of
output channels
3) Click here
for the mic
matching
result!

Customer Fill In
1. Microphone Matching Check - Results
Record your data here!
Q) Check Meter_Mic to see whether they are within +/-
1 dB. If not, write down the difference; if yes, write
down the median value.
If your microphones are not matched to within +/- 1 dB, you will lose
performance in beamforming. This can be helped with trim gains during
the tuning phase.

2. Microphone Sensitivity Check
• In Designer, double click the “MicSensitivity” triangle.
• Enter the microphone sensitivity from your spec sheet.
• Put this value as “offset”.
• Play the same sine tone at 75dBA described in the last
test.
• Double Click the “SPL_Display”.
• Verify that SPL levels shown match the SPL meter
reading.
Example

2. Mic Gain / Sensitivity RTASC-Lite.awd
5) Click here
for the
sensitivity
result!
4) Click
here to set
the offset!
Properties
Arguments
numOutChannels. To
output channels
3) Click here
for the mic
matching
result!

2. Microphone Sensitivity-Results
Customer Fill In
Q) Check Sink_SPL, and see whether the value
from Sink_SPL and that of the SPL meter are
within +/- 3 dB of each other. If not record!
If this reading doesn’t match the SPL meter, you should check
your driver microphone gain settings using something like
alsamixer –c0 (or c1/c2 etc... )

Microphone Acoustical Porting
MEMS
Mic
Vent
hole
Case
PCB
MEMS
Mic
Vent
hole
This is bad because if I block a
vent hole, the microphone
beneath it will still get sound
This is correct since each vent
hole only attaches to a single
microphones
MEMS
Mic
Case
PCB
MEMS
Mic
Gasket Gasket

• Play pink noise from an external speaker 20 cm above the
microphone array.
• Use the SPL meter at device mics to ensure the pink noise is
around 75 dBA at the device mics.
• Block a microphone by gently placing putty over the port.
• Verify that the digital level drops by at least 30 dB
• Repeat for all microphones
WARNING! Do not leave the mounting putty on top of the microphone for more than one hour. This makes it very difficult to clean up. When the
tests finish, gently wipe it out if necessary, while being careful not to touch or damage the microphone. Use caution if you must put putty directly
on a microphone, it may clog the port and/or damage the microphone.
Before Putty placed on mics
After Putty placed on mics

Click here for
the mic
isolation
result!
RTASC-Lite.awd

3. Microphone Isolation Test- Results Customer Fill In
Before Putty placed on mics
If you see less than 30dB of attenuation after placing the putty, then your
microphones are not properly sealed. Check to make sure there are no air
incorrect air leaks into the microphone chamber.

3. Microphone Isolation Test- Results
Customer Fill InAfter Putty placed on ch#01
microphones are not properly sealed. Check your gaskets for a good mechanical
fit.
After Putty placed on ch#02
Channel No# Drop Observed
Ch 01
Ch 02
Q) Verify that the dB values for each
microphone has dropped at least 30dB.

3. Microphone Isolation Test- Results
Customer Fill InAfter Putty placed on ch#03
microphones are not properly sealed. Check your gaskets for a good mechanical
fit.
After Putty placed on ch#04
Ch 03
Ch 04
Q) Verify that the dB values for each
microphone has dropped at least 30dB.

• You have 2 choices to perform this test
a. Cover all microphone vent holes with putty (preferred
method), or
b.Go to a quiet room or anechoic chamber
• No sound/tone required for this check.
• Look at the SPL_Display module and verify that it matches
the noise floor of the mic based on its data sheet.
• Example: microphone has 64 dB SNR per its datasheet.
You should measure a noise floor of:
94 - 64 = 30 dBA

Click here
for the mic
noise floor
result!
RTASC-Lite.awd

4. Mic Noise Floor Example
• No sound required for this test.
• Block each microphone with putty and measure
the corresponding noise floor in Designer.
• SPL meter measures ~35 dBA SPL (make sure you
use A-weighting and slow integration time)
• For ex: here Audio Weaver measures 47 dBA.
• There is 12 dB of extra noise in the system that
needs to be identified.
• Place YOUR measurements in the next slide
following this format.
Example Result
WARNING! Do not leave the mounting putty on top of the microphone for more than one hour. This makes it very difficult to clean up. When the
tests finish, gently wipe it out if necessary, while being careful not to touch or damage the microphone. Use caution if you must put putty directly
on a microphone, it may clog the port and/or damage the microphone.

Record your data Here!
4. Microphone Noise Floor-Results
Customer Fill In
Q) Check the value in the Sink_SPL to see if it
matches the noise floor in the datasheet (within +/-
1dB). Write down the value.
If the expected noise floor is not obtained in this test, it may be from circuit noise,
ultrasonic noise (mic filter should be fixed for this), microphone leakage, or something
else.

5. Loudspeaker THD
1. Use the same .awd as used in previous tests.
2. Play a 100 Hz sine wave at Full Volume from the
device using aplay.
3. Open up the inspector FreqResponse. This
shows the smoothed power response.
4. Set the module settings according to the dialog
box at 8000 as shown in Figure.
5. If there are harmonics in the spectrum, the
loudspeaker is distorting.
6. Repeat the procedures at 200 Hz, 300 Hz, and 1
kHz.
7. Take a snapshot of the FreqResponse inspector.
Click on
Advanced
to change
Freq

5. Loudspeaker THD
Click here for
the Freq
Response
result!
Properties Arguments
numOutChannels. To
output channels
RTASC-Lite.awd

Example for 300Hz
5. Loudspeaker THD – Result_Example
The maximum AEC performance equals the number of dB between the fundamental and
the largest harmonic. If there are other strong harmonics present than the AEC
performance will degrade even further.
Fundamental Peak
Largest Harmonic
Other Large Harmonics
Diff between fundamental
and largest harmonic =
Maximum AEC Performance

Customer Fill In for 100Hz
5. Loudspeaker THD – Result_1
Customer Fill In for 200Hz
Frequency Difference Observed
100 Hz
200 Hz
Q) Write down all the fundamental peak levels,
and the highest harmonic peak level for both

5. Loudspeaker THD – Result_2
Customer Fill In for 300Hz Customer Fill In for 1KHz
Frequency Difference Observed
300 Hz
1000 Hz
Q) Write down all the fundamental peak levels,
and the highest harmonic peak level for both

6. Conducted Sound
• This test measures how much sound is conducted from
the loudspeaker to the microphones through the
enclosure.
• Play pink noise from the device at 75dBA on the SPL
meter at the microphones.
• Take a Screenshot of the Mic_Only meter and paste it
into the results slide.
• Cover the microphone vent holes with putty
• Measure again and take screenshot and place it into the
results slide.
• Verify that there is a signal level drop of ≥ 6 dB in
Sink_SPL.
Before Putty After Putty
Example

6. Conducted Sound RTASC-Lite.awd
Click here for
the conducted
sound result!

Before Putty
Q) Did all signal levels drop at
least 6 dB? Write down the value
of drop at signal level.
AEC performance will suffer if there is conducted noise through the device which
indicates faulty microphone enclosure.
6. Conducted Sound - Results
After Putty

7. Reference Signal to Microphone Latency
• Play pink noise at 75dBA from the device using its internal speaker
• Check the LatencyPeak module for at least 15 minutes.
• LatencyPeakGraph shows this data over time.
• Take the measured Latency Peak Value and insert it into the Ref
LatencyControlSamples, if the Latency Peak becomes 0 than the delay
is in microphone receiver path otherwise it is in audio loopback.
• To confirm set the micLatencyControlSamps to
• 4096(max FFT window)-1560(Example Latency Peak Val) = 2536
• check if the LatencyPeak becomes 0.
• Jitter +/- 1 sample is OK due to measurement noise
• Large discontinuities or ramping delays are a problem
RTASC-Lite.awd

7. Reference Signal to Microphone Latency
2) Click here
for the
Latency
Peak Value
2) Click here
for the
Latency
Graph
3) D.Click here
to substitute
the Peak
Latency Value
in Ref Channel
3) D.Click here
to substitute
the Peak
Latency Value
in Mic Channel
1) Click here
for to
change the
reference
channel/s
1) Click here
for to
change the
microphone
channel
RTASC-Lite.awd

7. Reference Signal to Microphone Latency Results
Record your results
here!
Q) Does the Latency Peak
remain the same? Write down
the value.
Customer Fill In
Sudden drop in the latency peak graph indicates that drop out which
might be due to priority issues among software tasks, there might be
buffering issues, clocking issues like mics and DACs on different clock
domains or misconfigured sample rate converter which needs to be
fixed otherwise the Echo canceler performance will suffer.
Example Result

8. AEC Check
• Open AEC_Test.awd from your AWE Designer
• Play Pink Noise at 75dBA and repeat it again at near the max
volume of the device.
• Play it from the internal speaker using ‘aplay’ or Bluetooth.
• Set the RouteRef module to the audio reference channels by
double clicking it and set the Source to the appropriate audio
channels
• Click on NoiseReduction and AEC_Perf_Sink to view the results.
• Take screen shot of your results and paste it into the results slide.

8. AEC Check
1) Click here
for the Noise
Reduction
Results
2) Click here
to see the
AEC Graph
AEC_Test.awd

8. AEC Check –Results @ 75dB
Example Customer Fill In
This test can be used to tune the AEC and verify its operation.
The “Echo Return Loss Enhancement” (ERLE) shows the number of dB of AEC performance.
This varies over time based on the program material and the loudspeaker THD.
If you see a negative value in the Noise Reduction Window than contact DSP Concepts!
Q) Write down the value of
Noise Reduction

8. AEC Check –Results @ 100% Volume
Example Customer Fill In
This test can be used to tune the AEC and verify its operation.
The “Echo Return Loss Enhancement” (ERLE) shows the number of dB of AEC performance
which is Mic Signal - Signal after Echo Cancellation.
This varies over time based on the program material and the loudspeaker THD.
If you see a negative value in the Noise Reduction Window than contact DSP Concepts!
Q) Write down the value of
Noise Reduction
Mic Signal
Signal after Echo
Cancellation

dspconcepts.com
RTASC “Lite” Checks Complete!

RTASC Lite - Real Time Audio System Check Lite

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