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Add preemphasis and deemphasis

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This commit is contained in:
Geoffrey Merck 2020-05-08 21:16:02 +02:00
parent dc9e6ade23
commit bc22709abb
2 changed files with 13 additions and 5 deletions
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15
FMControl.cpp
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@ -20,14 +20,13 @@
#include <string>
const uint8_t BIT_MASK_TABLE[] = { 0x80U, 0x40U, 0x20U, 0x10U, 0x08U, 0x04U, 0x02U, 0x01U };
#define WRITE_BIT(p,i,b) p[(i)>>3] = (b) ? (p[(i)>>3] | BIT_MASK_TABLE[(i)&7]) : (p[(i)>>3] & ~BIT_MASK_TABLE[(i)&7])
#define READ_BIT(p,i) (p[(i)>>3] & BIT_MASK_TABLE[(i)&7])
#define EMPHASIS_GAIN_DB 0 //Gain needs to be the same for pre an deeemphasis
CFMControl::CFMControl(CFMNetwork* network) :
m_network(network),
m_enabled(false)
m_enabled(false),
m_preemphasis(0.3889703087993727F, -0.3290005228984741F, 0.0F, 1.0F, 0.282029168302153F, 0.0F, EMPHASIS_GAIN_DB),
m_deemphasis(1.0F, 0.282029168302153F, 0.0F, 0.3889703087993727F, -0.3290005228984741F, 0.0F, EMPHASIS_GAIN_DB)
{
assert(network != NULL);
}
@ -67,6 +66,9 @@ bool CFMControl::writeModem(const unsigned char* data, unsigned int length)
}
// De-emphasise the data and any other processing needed (maybe a low-pass filter to remove the CTCSS)
for(unsigned int i = 0U; i < nSamples; i++) {
samples[i] = m_deemphasis.filter(samples[i]);
}
unsigned char out[350U];
unsigned int nOut = 0U;
@ -102,6 +104,9 @@ unsigned int CFMControl::readModem(unsigned char* data, unsigned int space)
}
// Pre-emphasise the data and other stuff.
for(unsigned int i = 0U; i < nSamples; i++) {
samples[i] = m_preemphasis.filter(samples[i]);
}
// Pack the floating point data (+1.0 to -1.0) to packed 12-bit samples (+2047 - -2048)
unsigned int pack = 0U;

3
FMControl.h
View file

@ -21,6 +21,7 @@
#include "FMNetwork.h"
#include "Defines.h"
#include "IIRDirectForm1Filter.h"
class CFMControl {
public:
@ -38,6 +39,8 @@ public:
private:
CFMNetwork* m_network;
bool m_enabled;
CIIRDirectForm1Filter m_preemphasis;
CIIRDirectForm1Filter m_deemphasis;
};
#endif