A test apparatus for testing digitized test responses has a generator and a signal extractor. The generator uses direct digital synthesis to generate a set of n digital reference signals which are orthogonal to one another. In this case, n is a natural number greater than 1. The signal extractor contains a test input and reference inputs. The test input receives a digitized test response and the reference inputs are connected to the reference signals which are generated by the generator. The signal extractor generates scalar products from a respective reference signal and the test response and uses the products to calculate whether a combination of reference signals is contained in the test response.