Audio Solutions on the RX MCU Family

Renesas Electronics America Inc.

© 2012 Renesas Electronics America Inc. All rights reserved.

Class ID:

Audio Solutions on the RX MCU Family

Mitch Ferguson, Applications Engineering Manager

5L071

© 2012 Renesas Electronics America Inc. All rights reserved. 2 2

Mitch Ferguson

Applications Engineer Manager

Provides support of design teams using ADCs in MCU system.

Over 15 years of system-level design experience

Over 7 years of experience as an application engineer.

As a hardware engineer and engineering manager, he has been involved in design in power distribution controls, automotive and fire alarm systems with focus on analog design and EMI/EMS issues.

Bachelor of science in electrical engineering from Cleveland State University

© 2012 Renesas Electronics America Inc. All rights reserved. 3

Renesas Technology & Solution Portfolio


Microcontroller and Microprocessor Line-up

Wide Format LCDs Industrial & Automotive, 130nm

350µA/MHz, 1µA standby

44 DMIPS, True Low Power

Embedded Security, ASSP

165 DMIPS, FPU, DSC

1200 DMIPS, Performance 1200 DMIPS, Superscalar

500 DMIPS, Low Power

165 DMIPS, FPU, DSC

25 DMIPS, Low Power

10 DMIPS, Capacitive Touch

Industrial & Automotive, 150nm

190µA/MHz, 0.3µA standby

Industrial, 90nm


Automotive & Industrial, 90nm



600µA/MHz, 1.5µA standby Automotive, 40nm

500µA/MHz, 35µA deep standby

Industrial, 40nm


Industrial, 90nm

1mA/MHz, 100µA standby



2010 2013

32-b

it

8/1

6-b

it







165 DMIPS, FPU, DSC



165 DMIPS, FPU, DSC

25 DMIPS, Low Power




Industrial, 90nm







Industrial, 40nm


Industrial, 90nm




2010 2013

32-b

it

8/1

6-b

it







165 DMIPS, FPU, DSC



165 DMIPS, FPU, DSC

25 DMIPS, Low Power




Industrial, 90nm







Industrial, 40nm


Industrial, 90nm




2010 2013

32-b

it

8/1

6-b

it

32-Bit High Performance DSP, FPU with High Integration


‘Enabling The Smart Society’

Challenge: “Improving the interface to the new smart machines is one of the important concepts of the Smart Society. Audio is an effective way of improving information delivery”

Solution:

“This class will show you how simple it can be to add various levels of audio to your next project”


Agenda

Discuss audio formats and requirements

Embedded applications not high quality music players

Hardware Requirements

DAC

PWM

RX Audio Demo Components

Basic decoding scheme

Peripheral Blocks

Lab

Summary


Audio Experience

BMW pursuing better acoustics to improve efficiency

Audio used to compensate for low RPM rumble

- At Mercedes-Benz...engineers record the sounds of those servo motors used to raise the windows and adjust the seats, then compare them with sounds made by a BMW and other competitor

if it sounds well made, it probably is

Do Your Products Sound Priceless?

http://green.autoblog.com/2010/05/20/bmw-pursuing-better-acoustics-to-improve-efficiency/


Audio Considerations


Key Considerations

What type of audio is needed

Simple tones

Speech

Music

What are characteristics and requirements

File size

– Internal Flash

– External file storage

– File system

MCU and Bus Bandwidth

Transducer (speaker)

Amplifier/filter requirements


Sample Rates and Quality

8kHz, 8 bits

Telephone quality

11kHz

passable voice

22kHz, 8 bits,

good for a mix of mono speech and music.

44.1kHz , 16 bits

Good for audio and quality speech



Telephone or Voice quality

Bandwidth: 180 Hz to 3.2 kHz

Low end avoids 60 Hz region.

Noise pickup

Size of transformers

High end bandwidth issue

8 kHz sampling rate

sufficient for speech intelligibility

Signal to Noise: Approximately 45 dB

Human voice extends from 80 Hz to 14 kHz

Lab will investigate voice quality

Spectrum of Audio Clip


Bandwidth, Storage and Dynamic Range


Dynamic Range – How many bits?

48 dB = 8 bit

60 dB = 10 bit

96 dB = 16 bit

144 dB = 24 bit


Improving Dynamic Range Use signal compression techniques

u-Law or A-law

– 8 bit data, 8K sampling rate = 8kB/sec

– Compression ratio 2:1


Signal Compression - ADPCM

PCM stores digitized audio - WAVE is a PCM file

DPCM (Differentia) stores the difference from predicted last sample

ADPCM – Adaptive – adapts step size for better compression (4:1}


Audio Data Compression

Format (compression type) Bitrate (Kbps) Filesize (KB/min)

Uncompressed WAV 1411 105,000

MP3 128 960

MP3 (VBR) 112 840RA 96 720

WMA 92 690

OGG 112 840

MPC 88 660

AAC 80 600

AC3 967 720

Comparison Audio Files


Hardware requirements


DAC or PWM Output

Which is better?

DAC is simple

DAC resolution must be considered

DAC settling time may limit actual audio range

PWM very flexible, available on most MCUs

PWM resolution may be limited depending on carrier


Filter Considerations

DAC output should have filter

Basically same requirement as anti-aliasing filter on ADC

Should filter all frequencies above sampling rate/2

May cause amplitude distortion

Buffer and filter can be combined

Output resistance of the DAC should be considered in the filter design

Simple RC acceptable in many applications

Some systems like audio the speaker or listener filters many of the unwanted higher frequencies


PWM vs DAC Resolution

At 10 kHz DAC settling time (3 uS) should not be a problem so all 1024 states of 10 bit DAC available

Using 16 bit MTU timer

48 Mhz / 44.1 kHz = 1088

Can utilize more that 10 bits (1024)

Increased resolution just adds audio dynamic range

If a lower resolution audio is used interrupts can be “skipped” while still using PWM carrier



DAC Output Resistance

Important specification of DAC

Relatively high for many MCU DACs

May require buffering in many cases

Some MCUs have internal buffer

If no internal buffer

Rload >> Ro to prevent loading

Rload>2*Resolution* Ro for <1/2 bit error

Ro on RX63N is 3.6K

DAC

Ro Rload

Vload


DAC Filter

Frequency / Hertz

500m 1 2 5 10 20 50 100 200 500 1k 2k 5k 10k 20k 50k 100k

Gain

/

10m

20m

50m

100m

200m

500m

1

2.5 kHz First Order Filter

Typically first order filter not enough

Often use amplifier and filter


Filter Considerations

Time/mSecs 1mSecs/div

-0 1 2 3 4 5

V

-1.2

-1

-0.8

-0.6

-0.4

-0.2

-0

0.2

0.4

0.6

0.8

1


RX Audio Demo


Renesas RX63N RDK J-Link

debugger

Speaker

Stereo headphone

jack

LED

Ring

SD-Card

Graphics

LCD

User push

buttons

POT

VR1

MIC and

amplifier


RX Audio Demo

SD-Card stack & low-level drivers

FAT file system browser

Supports

MP3

WAV

ADPCM

Stereo PWM output

Software volume control

YRDK RX63N


© 2012 Renesas Electronics America Inc. All rights reserved. 29 © 2012 Renesas Electronics America Inc. All rights reserved.

RX Audio Demo - supported formats

MP3

MPEG-1/Audio(ISO/IEC11172-3)LayerIII

MPEG-2/Audio(ISO/IEC 13818-3)LayerIII

MPEG-2.5 (For Low Sampling Frequencies)

ADPCM

WAV (uncompressed PCM)

16-bit stereo or mono ( 1 or 2 channels)

Sample rates (kHz)

44.1, 33.075, 22.05, 11.025


RX Audio Demo Decode path block diagram

SD-Card

RSPI MMC FAT MP3 Render

Raw binary Blocks File I/O MP3

decode Timers


RX Audio Demo

Rendering block diagram

Render

Ping

Pong

DTC TPU

L

R

Sample Rate

Ready for next PCM data sample

Reload

Load next PCM sample


Timer Operation

Timer count value

Elapsed time

TPU1.TGRB

TPU0.TGRA

TPU0.TGRB

TPU1.TGRB clears all channels at the audio sample rate

Channel A PWM

Channel B PWM

Sets Playback Rate


RX Audio Demo

MCU peripherals used

Two synchronizable "TPU" timer channels for PWM

audio rendering.

Data Transfer Controller (DTC) for streaming PWM

timer data to the TPU timers.

RSPI channel for SDCard communication

12-bit ADC to measure the potentiometer setting

for audio playback volume

1 Compare Match Timer (CMT) channel for timed

delays in SDCard driver code

Real-time clock (RTC)--used for file time stamp


Lab Time !


Summary

Audio formats and requirements

How good is “voice quality”

Hardware

DAC

PWM

Audio

Various quality levels depending on need

Trade-off

– File storage size

– Decode bandwidth

– Quality


Questions?


‘Enabling The Smart Society’

Challenge: “Improving the interface to the new smart machines is one of the important concepts of the Smart Society. Audio is one of the most effective ways of improving information delivery”

Solution:

“This class will show you how simple it can be to add various levels of audio to your next project”


Please utilize the ‘Guidebook’ application to leave feedback

or

Ask me for the paper feedback form for you to use…

Please Provide Your Feedback…

Renesas Electronics America Inc.


Audio Solutions on the RX MCU Family

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Transcript of Audio Solutions on the RX MCU Family