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#130 MPT-1327 Decoder Filter issue resolved. Converts the post-demodulation filter from a band pass filter to a low-pass filter with 60 dB attenuation and a cutoff of 3200 Hz. This is then followed by a high-pass filter at the decimated channel rate, internal to the decoder that performs DC removal and removes any CTCSS tones prior to the FSK decoder.

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This commit is contained in:
Denny
2017-01-24 20:26:57 -05:00
parent 8b403e6d87
commit 1786ffac47
3 changed files with 83 additions and 53 deletions
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74
src/module/decode/mpt1327/MPT1327Decoder.java
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@@ -21,8 +21,9 @@ package module.decode.mpt1327;
import alias.AliasList;
import bits.MessageFramer;
import bits.SyncPattern;
import dsp.filter.FilterFactory;
import dsp.filter.Filters;
import dsp.filter.dc.DCRemovalFilterLyons;
import dsp.filter.fir.FIRFilterSpecification;
import dsp.filter.fir.real.RealFIRFilter_RB_RB;
import dsp.filter.halfband.real.HalfBandFilter_RB_RB;
import dsp.fsk.FSK2Decoder;
@@ -55,6 +56,30 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
{
private final static Logger mLog = LoggerFactory.getLogger(MPT1327Decoder.class);
private static final FIRFilterSpecification HIGH_PASS_SPECIFICATION = FIRFilterSpecification.highPassBuilder()
.sampleRate( 24000 )
.stopBandCutoff( 800 )
.stopBandAmplitude( 0.0 )
.stopBandRipple( 0.03 )
.passBandStart( 1000 )
.passBandAmplitude( 1.0 )
.passBandRipple( 0.08 )
.build();
private static float[] HIGHPASS_FILTER;
static
{
try
{
HIGHPASS_FILTER = FilterFactory.getTaps(HIGH_PASS_SPECIFICATION);
}
catch(Exception e)
{
mLog.error("Couldn't design MPT1327 highpass filter");
}
}
/* Decimated sample rate ( 48,000 / 2 = 24,000 ) feeding the decoder */
private static final int sDECIMATED_SAMPLE_RATE = 24000;
@@ -66,17 +91,16 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
private static final int sMESSAGE_LENGTH = 350;
/* Instrumentation Taps */
private static final String INSTRUMENT_HB1_FILTER_TO_LOW_PASS =
private static final String INSTRUMENT_HB1_FILTER_TO_HIGH_PASS =
"Tap Point: Half-band Decimation Filter > < Low Pass Filter";
private static final String INSTRUMENT_LOW_PASS_TO_DECODER =
private static final String INSTRUMENT_HIGH_PASS_TO_DECODER =
"Tap Point: Low Pass Filter > < Decoder";
private static final String INSTRUMENT_DECODER_TO_FRAMER =
"Tap Point: Decoder > < Sync Detect/Message Framer";
private List<TapGroup> mAvailableTaps;
private HalfBandFilter_RB_RB mDecimationFilter;
private RealFIRFilter_RB_RB mLowPassFilter;
private DCRemovalFilterLyons mDCRemovalFilter;
private RealFIRFilter_RB_RB mHighPassFilter;
private FSK2Decoder mFSKDecoder;
private Broadcaster<Boolean> mSymbolBroadcaster;
private MessageFramer mControlMessageFramer;
@@ -85,9 +109,6 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
public MPT1327Decoder(AliasList aliasList, Sync sync)
{
/* Decimation filter - 48000 / 2 = 24000 output */
mDecimationFilter = new HalfBandFilter_RB_RB(Filters.FIR_HALF_BAND_31T_ONE_EIGHTH_FCO.getCoefficients(), 1.0002f, true);
/**
* Normal: 2FSK Decoder with inverted output
* French: 2FSK Decoder with normal output
@@ -105,7 +126,15 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
throw new IllegalArgumentException("MPT1327 Decoder - unrecognized Sync type");
}
mDecimationFilter.setListener(mFSKDecoder);
/* Decimation filter - 48000 / 2 = 24000 output */
mDecimationFilter = new HalfBandFilter_RB_RB(Filters.FIR_HALF_BAND_31T_ONE_EIGHTH_FCO.getCoefficients(), 1.0002f, true);
//High-pass filter the audio to remove any DC component or CTCSS tones. The audio has already been low-pass
//filtered by the AudioDemodulation filter cutoff of 3400 Hz.
mHighPassFilter = new RealFIRFilter_RB_RB(HIGHPASS_FILTER, 1.0f);
mDecimationFilter.setListener(mHighPassFilter);
mHighPassFilter.setListener(mFSKDecoder);
mSymbolBroadcaster = new Broadcaster<Boolean>();
mFSKDecoder.setListener(mSymbolBroadcaster);
@@ -148,17 +177,10 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
mControlMessageFramer.dispose();
if(mDCRemovalFilter != null)
{
mDCRemovalFilter.dispose();
}
mFSKDecoder.dispose();
mDecimationFilter.dispose();
mLowPassFilter.dispose();
mMessageProcessor.dispose();
mTrafficMessageFramer.dispose();
@@ -174,8 +196,8 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
TapGroup group = new TapGroup("MPT-1327 Decoder");
group.add(new FloatTap(INSTRUMENT_HB1_FILTER_TO_LOW_PASS, 0, 0.5f));
group.add(new FloatTap(INSTRUMENT_LOW_PASS_TO_DECODER, 0, 0.5f));
group.add(new FloatTap(INSTRUMENT_HB1_FILTER_TO_HIGH_PASS, 0, 0.5f));
group.add(new FloatTap(INSTRUMENT_HIGH_PASS_TO_DECODER, 0, 0.5f));
group.add(new BinaryTap(INSTRUMENT_DECODER_TO_FRAMER, 0, 0.025f));
mAvailableTaps.add(group);
@@ -195,14 +217,14 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
switch(tap.getName())
{
case INSTRUMENT_HB1_FILTER_TO_LOW_PASS:
case INSTRUMENT_HB1_FILTER_TO_HIGH_PASS:
FloatBufferTap hb1Tap = (FloatBufferTap) tap;
mDecimationFilter.setListener(hb1Tap);
hb1Tap.setListener(mLowPassFilter);
hb1Tap.setListener(mHighPassFilter);
break;
case INSTRUMENT_LOW_PASS_TO_DECODER:
case INSTRUMENT_HIGH_PASS_TO_DECODER:
FloatBufferTap lowTap = (FloatBufferTap) tap;
mLowPassFilter.setListener(lowTap);
mHighPassFilter.setListener(lowTap);
lowTap.setListener(mFSKDecoder);
break;
case INSTRUMENT_DECODER_TO_FRAMER:
@@ -220,11 +242,11 @@ public class MPT1327Decoder extends Decoder implements IFilteredRealBufferListen
switch(tap.getName())
{
case INSTRUMENT_HB1_FILTER_TO_LOW_PASS:
mDecimationFilter.setListener(mLowPassFilter);
case INSTRUMENT_HB1_FILTER_TO_HIGH_PASS:
mDecimationFilter.setListener(mHighPassFilter);
break;
case INSTRUMENT_LOW_PASS_TO_DECODER:
mLowPassFilter.setListener(mFSKDecoder);
case INSTRUMENT_HIGH_PASS_TO_DECODER:
mHighPassFilter.setListener(mFSKDecoder);
break;
case INSTRUMENT_DECODER_TO_FRAMER:
mFSKDecoder.setListener(mSymbolBroadcaster);