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An extensible C++ testing abstraction for audio signals

AudioTraits is an abstraction designed to make testing of audio processing more convenient and readable. An 'Audio Trait' analyzes a given audio signal (some or all of its channels) and checks for a certain property. The result of this check is boolean, which allows this to be easily integrated in any unit test framework.

AudioTraits is easily extensible - users can define their own traits and signal adapters.

In the testing landscape, AudioTraits is meant to go somewhere between basic instantiation-only and fully-fledged numerical precision tests (e.g. comparison against reference data)

• What it was designed for: testing the logic and functionality of audio blocks with idiomatic code
• What it was NOT designed for: precision, performance, efficiency, use in production code

Usage Example

#include "AudioTraits.hpp"
using namespace slb;
using namespace AudioTraits; // for convenience

// Assume buffer contains some data with dimensions [channels=6][samples=16] 
std::vector<std::vector<float>> buffer = { ... };
SignalAdapterStdVecVec signal(buffer);

// Check if there is signal present (time domain)
REQUIRE(check<HasSignalOnAllChannels>(signal, {})); // signal on all channels 
REQUIRE(check<HasSignalOnAllChannels>(signal, {1,2})); // signal on channels 1 and 2
REQUIRE(check<HasSignalOnAllChannels>(signal, {1, 2, {4,6}}));  // signal on channels 1, 2 and 4-6
REQUIRE(check<HasSignalOnAllChannels>(signal, {5}, -40.f)); // signal on chan 5 is above -40dB

// Check if a signal is a delayed version of another 
// (tolerance for delay and amplitude can be adjusted)
SignalAdapterStdVecVec delayedSignal = ...; // assume this is 'signal' delayed by 4 samples
REQUIRE(check<IsDelayedVersionOf>(signal, {}, delayedSignal, 4));
REQUIRE_FALSE(check<IsDelayedVersionOf>(signal, {}, delayedSignal, 2));

// Frequency-Domain Traits:
constexpr float sampleRate = 48000;

// signal on chan 1 has content at around 1000Hz
REQUIRE(check<HasSignalInAllBands>(signal, {1}, Freqs{1000}, sampleRate));
// signal has content in the band 500Hz-1000Hz in all channels
REQUIRE(check<HasSignalInAllBands>(signal, {}, Freqs{500, 1000}, sampleRate));
// signal has content in 100Hz-200Hz that is -30dB below the maximum over the entire spectrum
REQUIRE(check<HasSignalInAllBands>(signal, {}, Freqs{100, 200}, sampleRate, -30.f));

// signal only has content above -5dB in the band 20-5000 Hz (relative to the spectral maximum)
REQUIRE(check<HasSignalOnlyInBands>(signal, {}, Freqs{20, 5000}, sampleRate, -5.f));
// signal only has content below 4kHz in all channels
REQUIRE(check<HasSignalOnlyBelow>(signal, {}, 4000, sampleRate));

NOTE: For the frequency-domain traits, a 4096-point FFT is calculated for every single check. This is - needless to say - very inefficient, but a conscious design choice for the sake of simplicity. Adding more optimized, stateful 'traits' is quite easy, should there be a need.

Extension: Custom Traits

Defining custom traits is very straightforward: a traits is simply a functor with a static (stateless) function that returns a boolean:

#include "AudioTraits.hpp"
struct HasOddNumberOfSamples
{
    static bool eval(const ISignal& signal, const std::set<int>& selectedChannels)
    {
        if (signal.getNumSamples() % 2 == 0) {
            return false; // number of samples is even
        } else {
            return true; // number of samples is odd
        }
    }
};

• The number of parameters of the eval() is variable, so a custom trait may add any number of additional parameters besides signal and selectedChannels.

• ISignal is the common interface for all signal to be analyzed. A signal is a minimalistic 2-dimensional construct with a number of channels and samples.

• Signal 'adapters' are pre-defined for raw pointers (e.g. float**) and std::vector<std::vector<T>>, and additional adapters can easily be added for other audio signal sources.

Requirements / Compatibility

• C++14, STL only
• Compiled & Tested with:
  • Linux / macos / Windwos
  • GCC, Clang and MSVC
  • x86_64 and arm64 architectures

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