TIME & FREQUENCY DOMAIN OF TRANSMITTED & RECIEVED SIGNAL

[CoinLAb10]

Dear Georgi

Your work is amazing, i fallowed your guidelines on how to build and test this library it worked.

i was curious on how to save the received waveform/signal so that one can analyze and draw the Time domain of the signal which can help to see the effect of noise when compared to the transmitted signal.

i have seen that you do have the section that save transmitted signal as .wav.

thank you

[ayzic45]

This should be done, by playing with the SDL library, to save the waveform of the signal being encoded or decoded. and PHP makes it easier, you can actually export the recorded/captured data before doing anything with it. then use MATLAB analyzing and graph plots(Time & Frequency Domain), a piece of code from MATLAB forum can help plot the graph in MATLAB.

all be best.

[ggerganov]

That is correct. The received waveform/signal is obtained directly from SDL or the respective audio backend that you use to capture the data. ggwave is not needed in order to plot the Time domain data of the recorded audio - you simple need to process the RAW captured samples.

In case you want to plot the transmitted audio waveform, then you can obtain it via GGWave::takeTxAmplitudeI16() method after calling the GGWave::encode() method. See the Waver app for example:

ggwave/examples/waver/common.cpp

Lines 703 to 706 in 43bf2f1

	if (ggWave->takeTxAmplitudeI16(g_buffer.stateCore.txAmplitude)) {
	g_buffer.stateCore.update = true;
	g_buffer.stateCore.flags.newTxAmplitude = true;
	}

And plotting:

ggwave/examples/waver/common.cpp

Lines 1478 to 1532 in 43bf2f1

	static float amax = 0.0f;
	static float frac = 0.0f;
	amax = 0.0f;
	frac = (ImGui::GetTime() - tStartTx)/tLengthTx;
	if (txAmplitudeDataCurrent.size() && frac <= 1.0f) {
	struct Funcs {
	static float Sample(void * data, int i) {
	auto res = std::fabs(((int16_t *)(data))[i]) ;
	if (res > amax) amax = res;
	return res;
	}
	static float SampleFrac(void * data, int i) {
	if (i > frac*txAmplitudeDataCurrent.size()) {
	return 0.0f;
	}
	return std::fabs(((int16_t *)(data))[i]);
	}
	};
	auto posSave = ImGui::GetCursorScreenPos();
	auto wSize = ImGui::GetContentRegionAvail();
	wSize.x = ImGui::GetContentRegionAvailWidth() - ImGui::CalcTextSize(sendButtonText).x - 2*style.ItemSpacing.x;
	wSize.y = ImGui::GetTextLineHeight();
	ImGui::PushStyleColor(ImGuiCol_FrameBg, { 0.3f, 0.3f, 0.3f, 0.3f });
	ImGui::PushStyleColor(ImGuiCol_PlotHistogram, ImGui::GetStyleColorVec4(ImGuiCol_TextDisabled));
	ImGui::PlotHistogram("##plotSpectrumCurrent",
	Funcs::Sample,
	txAmplitudeDataCurrent.data(),
	(int) txAmplitudeDataCurrent.size(), 0,
	(std::string("")).c_str(),
	0.0f, FLT_MAX, wSize);
	ImGui::PopStyleColor(2);
	ImGui::SetCursorScreenPos(posSave);
	ImGui::PushStyleColor(ImGuiCol_FrameBg, { 0.0f, 0.0f, 0.0f, 0.0f });
	ImGui::PushStyleColor(ImGuiCol_PlotHistogram, { 0.0f, 1.0f, 0.0f, 1.0f });
	ImGui::PlotHistogram("##plotSpectrumCurrent",
	Funcs::SampleFrac,
	txAmplitudeDataCurrent.data(),
	(int) txAmplitudeDataCurrent.size(), 0,
	(std::string("")).c_str(),
	0.0f, amax, wSize);
	ImGui::PopStyleColor(2);
	} else {
	if (settings.isFixedLength) {
	ImGui::TextDisabled("Listening for waves (fixed-length %d bytes)", settings.payloadLength);
	} else {
	ImGui::TextDisabled("Listening for waves (variable-length)");
	}
	}