Move minimum frequency check to modem checkSampleRate()

src/modules/modem/ModemAnalog.cpp

@@ -9,6 +9,9 @@ std::string ModemAnalog::getType() {
 }
 
 int ModemAnalog::checkSampleRate(long long sampleRate, int audioSampleRate) {
+    if (sampleRate < 1500) {
+        return 1500;
+    }
     return sampleRate;
 }
 

src/modules/modem/ModemDigital.cpp

@@ -9,6 +9,9 @@ std::string ModemDigital::getType() {
 }
 
 int ModemDigital::checkSampleRate(long long sampleRate, int audioSampleRate) {
+    if (sampleRate < 1500) {
+        return 1500;
+    }
     return sampleRate;
 }
 

src/modules/modem/analog/ModemFMStereo.cpp

@@ -33,6 +33,8 @@ Modem *ModemFMStereo::factory() {
 int ModemFMStereo::checkSampleRate(long long sampleRate, int audioSampleRate) {
     if (sampleRate < 100000) {
         return 100000;
+    } else if (sampleRate < 1500) {
+        return 1500;
     } else {
         return sampleRate;
     }

src/modules/modem/analog/ModemLSB.cpp

@@ -20,6 +20,9 @@ ModemLSB::~ModemLSB() {
 }
 
 int ModemLSB::checkSampleRate(long long sampleRate, int audioSampleRate) {
+    if (sampleRate < 1500) {
+        return 1500;
+    }
     if (sampleRate % 2 == 0) {
         return sampleRate;
     }

src/modules/modem/analog/ModemUSB.cpp

@@ -20,6 +20,9 @@ ModemUSB::~ModemUSB() {
 }
 
 int ModemUSB::checkSampleRate(long long sampleRate, int audioSampleRate) {
+    if (sampleRate < 1500) {
+        return 1500;
+    }
     if (sampleRate % 2 == 0) {
         return sampleRate;
     }