diff options
Diffstat (limited to 'host')
| -rw-r--r-- | host/examples/wavetable.hpp | 43 |
1 files changed, 24 insertions, 19 deletions
diff --git a/host/examples/wavetable.hpp b/host/examples/wavetable.hpp index 216fe5012..dc2a93c36 100644 --- a/host/examples/wavetable.hpp +++ b/host/examples/wavetable.hpp @@ -1,7 +1,7 @@ // // Copyright 2010-2012,2014 Ettus Research LLC // Copyright 2018 Ettus Research, a National Instruments Company -// Copyright 2019 Ettus Research, A National Instruments Brand +// Copyright 2019-2020 Ettus Research, A National Instruments Brand // // SPDX-License-Identifier: GPL-3.0-or-later // @@ -11,6 +11,7 @@ #include <stdexcept> #include <string> #include <vector> +#include <algorithm> static const size_t wave_table_len = 8192; @@ -18,35 +19,39 @@ class wave_table_class { public: wave_table_class(const std::string& wave_type, const float ampl) - : _wave_table(wave_table_len) + : _wave_table(wave_table_len, {0.0, 0.0}) { - // compute real wave table with 1.0 amplitude - std::vector<float> real_wave_table(wave_table_len); + // Note: CONST, SQUARE, and RAMP only fill the I portion, since they are + // amplitude-modulating signals, not phase-modulating. if (wave_type == "CONST") { - for (size_t i = 0; i < wave_table_len; i++) - real_wave_table[i] = 1.0f; + // Fill with I == ampl, Q == 0 + std::fill( + _wave_table.begin(), _wave_table.end(), std::complex<float>{ampl, 0.0}); } else if (wave_type == "SQUARE") { - for (size_t i = 0; i < wave_table_len; i++) - real_wave_table[i] = (i < wave_table_len / 2) ? 0.0f : 1.0f; + // Fill the second half of the table with ampl, first half with + // zeros + std::fill(_wave_table.begin() + wave_table_len / 2, + _wave_table.end(), + std::complex<float>{ampl, 0.0}); } else if (wave_type == "RAMP") { - for (size_t i = 0; i < wave_table_len; i++) - real_wave_table[i] = 2.0f * i / (wave_table_len - 1) - 1.0f; + // Fill I values with ramp from -1 to 1, Q with zero + for (size_t i = 0; i < wave_table_len; i++) { + _wave_table[i] = {(2.0f * i / (wave_table_len - 1) - 1.0f) * ampl, 0.0}; + } } else if (wave_type == "SINE") { static const double tau = 2 * std::acos(-1.0); + static const std::complex<float> J(0, 1); + // Careful: i is the loop counter, not the imaginary unit for (size_t i = 0; i < wave_table_len; i++) { - real_wave_table[i] = - static_cast<float>(std::sin((tau * i) / wave_table_len)); + // Directly generate complex sinusoid (a*e^{j 2\pi i/N}). We + // create a single rotation. The call site will sub-sample + // appropriately to create a sine wave of it's desired frequency + _wave_table[i] = + ampl * std::exp(J * static_cast<float>(tau * i / wave_table_len)); } } else { throw std::runtime_error("unknown waveform type: " + wave_type); } - - // compute i and q pairs with 90% offset and scale to amplitude - for (size_t i = 0; i < wave_table_len; i++) { - const size_t q = (i + (3 * wave_table_len) / 4) % wave_table_len; - _wave_table[i] = - std::complex<float>(ampl * real_wave_table[i], ampl * real_wave_table[q]); - } } inline std::complex<float> operator()(const size_t index) const |