Chapter 2 Improved Audio Template

7/28/2019 Chapter 2 Improved Audio Template

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2010 Texas Instruments Inc

Practical Audio Experiments using the TMS320C5505 USB Stick

ImprovedAudio Template

Texas Instruments University Programme

Teaching Materials


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Chapter 2 - Slide 2 2010 Texas Instruments Inc

Improved Audio Template


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Introduction

The code in MyFirstProject had:

Fixed sampling rate of 48000 samples per second

Suitable for line inputs (CD, iPod) onlyNot suitable for microphones and electric guitars.


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Objectives

To design an Improved Audio Template with:

Sampling rate adjustable between 8000 samplesper second and 48000 samples per second

Adjustable gain suitable for:

line inputs (CD player, MP3 etc).

microphones

electric guitars.


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What you will Learn

How to read TI datasheets and use the values toconfigure registers.

How to change the sampling rate and audio gain ofthe coder-decoder (CODEC)

How to use decibels.


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Setting up the Codec


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USB Stick Codec

Codec 12 MHz Crystal



Setting up the Codec

The TMS320C5505 USB Stick uses aTLV320AIC3204 Codec (coder-decoder).

The information required to configure this device is

contained in TI datasheet SLOS602A.



Codec Adjustments

The following can be adjusted on the codec:

Sampling rate

Input ADC gain

Output DAC gain.



Phase Locked Loop (PLL) Setup

Table 5-25 PLL gives example configurations.

This is the really useful part of the document!



Registers

All the fields PLLP, PLLR etc refer to specificregisters inside the Codec.

This phase lock loop (PLL) has:

a fixed oscillator on the outside (12 MHz)

lower speed operation on the inside (e.g. 48kHz).



Clock Distribution Tree

The clocksignals form atree.



PLL Loop Clock Setups

The Phase Locked Loop frequency is calculated asfollows:



Master Clock (MCLK)

The TMS320C5505 USB Stick uses a 32768 Hz crystal for the

Master Clock (MCLK).

The setup for 100 MHz is given in red.



Setting the ADC Gain

Microphones and guitars have low electrical output.

Additional gain is required for these devices.



Setting the ADC Gain

The ADC gain is controlled by Register 59 andRegister 60:


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Range of Gain Values

The TLV320AIC3204 supports gains between 0 dBand 47.5 dB.

In practical terms, intervals of 1 dB are perfectlyadequate.

This also solves the problem of expressing 0.5 dBusing fixed-point maths.


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Gain in Decibels

The gain is expressed in terms of decibels (dB).

A decibel is a ratio.

)(log20dBinGainReference

Input

10


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Useful Decibels

The following are decibel values and their ratioequivalents:

0 dB => 1:1

6 dB => 2:1

20 dB => 10:1

40 dB => 100:1

60 dB => 1000:1


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C Code Implementation


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New Function

The following C code function has been added toAIC3204_init.c

set_sampling_frequency_and_gain();

This function takes two parameters: unsigned long SamplingFrequency; // Sampling

frequency Hz

unsigned int ADCgain; // Gain in dB


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Sampling Frequencies

The sampling frequency can be any of the following:

48000

24000

16000

12000

9600

8000

6857

The default is 48000 Hz.


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New #define


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Electret Microphone

The TMS320C5505 USB Stick supports electretmicrophones.

It is necessary to turn on the MICBIAS power supply

Add the following line to aic3204_init.c:

AIC3204_rset(51, 0x40); // Enable MICBIAS


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Configuration Example

To configure the codec with:

Sampling frequency 48000 Hz

Gain 0dB

Use following #defines in main.c:

#define SAMPLES_PER_SECOND 48000

#define GAIN_IN_dB 0


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New Program Descriptors


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New Timed Steps

The TMS320C5505 has no switches, so Step changesonce every 20 seconds and flashes the XF LED.


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Introduction to Laboratory


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Installing the Application

Use the code given in Application 2 ImprovedAudio Template

Follow the steps previously given in Chapter 1 to

set up the new project.


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Create New Project


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Files Used in Project


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Line Setup TMS320C5505

USB to PC

Headphones

CD Player orMP3 Player

USB Stick


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Console for Line Setup

Sampling frequency and Gain are shown in theConsole window.


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Microphone Setup TMS320C5505

USB to PC

Headphones

Microphone


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Microphone Setup inmain.c

Change lines containing SAMPLES_PER_SECOND andGAIN_IN_dB as shown below:


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Console for Microphone Setup

New Sampling frequency and Gain are shown in theConsole window.


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Experiments


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Change Sampling Frequency

Try different values of sampling frequency bychanging the number in both main.c andLEDflasher.c:

#define SAMPLES_PER_SECOND 24000L


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Change Gain

Try different values of gain by changing thenumber in main.c:

#define GAIN_IN_dB 25


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Programming Challenge

Add code for Step 4 in main.c


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Using TI Datasheets


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Using TI Datasheets

The datasheet for the TLV320AIC3204 Codec hasthe TI literature number SLOS62A.

The last letter A is the revision number, which may

change.

Therefore, when searching for the latest version ofthe above document on the TI website, just enterSLOS62.


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References

TLV320AIC3204 Stereo Codec Data Sheet SLOS62.

Chapter 2 Improved Audio Template

Documents

Transcript of Chapter 2 Improved Audio Template