Digital Signal Processing with
LabVIEW 8.6
Lab # 07
Introduction to Digital Signal Processors
and Processing
Designed by
Adnan Niazi
Lab Engineer
Signal Processing/Signal & Systems Lab
CECOS University of IT & Emerging Sciences
27th- 28th March 2009
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Agenda
▌ Types of ADCs and DACs
▌ ADC and DAC of Speedy 33 Kit
▌ Designing an Audio VU meter
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Speedy-33 Architecture
When Audio in
Connector is
plugged in
When Audio in
Connector is
Disconnected
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
PCM3003
▌ PCM3003 is a stereo audio Codec
▌ Audio codec compresses High Fidelity audio signals so
as to have minimum number of bits without sacrificing
audio quality
▌ PCM3003 contains Sigma-Delta ADC and DAC
▌ Sigma delta ADCs and DACs are ideal for audio
applications because of their high precision and built-in
filtering
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Why Σ∆ ADC/DAC in Speedy-33
▌ There are three types of ADC
Flash ADC or Direct-Conversion ADC
• Very fast sampling rates (1GSPS)
• Very low resolution usually 8-bits or 12bit maximum
• Used in very high data rate applications such as
Oscilloscopes and Spectrum analyzer
• Audio must be represented by 16bits or more so that’s
why Flash ADC is not the correct choice
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Why Σ∆ ADC/DAC in Speedy-33
SAR (Successive Approximation ADC)
• Moderate Sampling Rates (1 MSPS)
• Moderate resolutions usually 16-18bits
• Used for motor control and industrial application
• They don’t have any built-in filtering that’s why they are
not preferred in audio application
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Why Σ∆ ADC/DAC in Speedy-33
Σ∆ or ∆Σ ADC
• Very high resolution 16-24bits
• Very low sample rate (256KSPS)
• Used in very high fidelity and very sensitive
applications such as Audio,
EEG(Electroencephalogram),
ECG(Electrocardiogram), ECoG (Elecrtocorticogram),
EMG(Elecrtomyogram)
• Built-in digital filtering in these ADC is an extra bonus
• That’s why Speedy-33 kit is using PCM3003 chip
which employs Σ∆ ADC and DAC
008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Audio VU Meter
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
Designing an Audio VU Meter
▌ VU is an essential part of audio equipments
▌ A VU meter displays the RMS value of the sound signal
▌ Instead of Instantaneous display of the volume level it
displays a smoothed out version of the volume
▌ A volume unit is equal to number of dbm above the
reference power level of 1dbm
©2008-2009 All rights reserved.
CECOS University of IT & Emerging Sciences
