Information about the varius stimulus options in SoundCheck
SoundCheck offers a selection of stimulus signal types (all of which can be user configured through the stimulus editor) including .wav files. This means that any user-defined test signal can be used.
Audio Test Stimuli offered in SoundCheck audio test and measurement software include Stweep (Listen’s frequency stepped sine sweep), frequency log sweep, log amplitude sweep, pink noise, white noise, MLS noise, multitone, intermodulation two tone, difference frequency two tone, speech or music based signals (WAV files) and composite stimulus signals. These are detailed below.
Stweep™ (Frequency stepped-sine sweep)
Stweep – stepped sine sweep
Stweep is Listen’s optimized stepped sine excitation signal. A conventional stepped sine stimulus plays a sine wave at discrete frequencies, step by step, within a frequency range specified by the user. The Stweep is a stepped-sine sweep that uses an integer number of cycles at each frequency step, ensuring a smooth, and phase continuous transition from frequency to frequency. This reduces abrupt changes in the test signal and thus reduces ringing in the transducer when changing frequencies. This ensures significantly less transducer settling time which results in faster and more accurate measurements. The figure below shows the difference between a classic stepped sine excitation and the Stweep test signal. Soundcheck permits linear, logarithmic or user-defined resolution, for example 1/3rd octave from 20 to 200Hz and 1/12th Octave from 200 to 20kHz).
Frequency Log Sweep (also known as Log Chirp or Farina method)
Frequency Log Sweep StimulusFrequency Log Sweep is a continuous log sine sweep from low to high. It uses the same time (and energy) for every octave, which achieves a good signal to noise ratio for all frequencies in typical electro-acoustical measurements. It is a good choice for production line loudspeaker testing as distortion is accurately measured at low frequencies while retaining a fast test speed and high throughput. It is also used for simulated free-field measurements by calculating the impulse response and time windowing out the room reflections (read a paper on simulated free field measurements using this technique). SoundCheck was the first commercial implementation of a harmonic, time-selective response using a Log chirp stimulus, just months after Angelo Farina’s landmark AES paper on the subject in 2000.
Log Amplitude Sweep
Log Amplitude Sweep StimulusA Log amplitude sweep is similar to a stepped sine sweep except a single frequency is chosen and swept through various levels. It may sweep from low to high, or high to low. It can also be used in conjunction with the Harmonictrak algorithm to look at characteristics like THD vs. stimulus level, which will produce a curve that has % distortion on the y-axis and stimulus level on the x axis. This is ideal for looking at Input vs. Output and compression curves.
Pink or White NoiseNoise
SoundCheck offers Pink, White and MLS noise stimuli with scalable Duration(s) and Band limits: Fmin and Fmax.
Pink noise is noise with a continuous frequency spectrum and with equal power per constant percentage bandwidth. For example, equal power in any one-third octave band. Like a Log Sweep, it is recommended for electro-acoustical measurements.
White noise is noise with a continuous frequency spectrum and with equal power per unit bandwidth. For example, equal power in any band of 100-Hz width. It is recommended for electrical measurements.
MLS noise is a noise signal with a very low crest factor used in the MLSSA system and is offered in SoundCheck to enable comparison with older measurement systems.
A multitone stimulus consists of multiple sine tones of discrete frequencies played simultaneously with equal amplitudes and optimized phase for low crest-factor. All the frequencies are present at the same time (in contrast to the stepped sine sweep where the frequencies are present sequentially) which allows very fast measurements. SoundCheck’s multitone stimulus uses frequency rounding to ensure that there will be an FFT line at every tone frequency.
Two tone stimuli Intermodulation Stimulus
Two tone stimuli play 2 different tones simultaneously. This stimulus is useful to measure distortion in band-limited devices like hearing aids, phones, and loudspeakers. It can also be useful for measuring distortion in microphones by using a separate loudspeaker to play each tone. This isolates the harmonic distortion coming from the loudspeakers and measures the resulting IM distortion coming from the microphone (read a paper on distortion measurements). SoundCheck offers two types of two-tone stimulus:
Intermodulation Two-tone Stimulus
The intermodulation stimulus is a stepped sine sweep superimposed on top of a fixed frequency tone. The fixed tone is usually a low frequency tone set near the resonance frequency of the loudspeaker and the sweeping frequency is usually higher.
Difference Frequency Stimulus
Difference Frequency two-tone Stimulus
The difference frequency stimulus is composed of two sweeping tones separated by a specified frequency interval which may be a fixed difference or a fixed ratio.
Speech or Music based Signals: WAV file (Windows audio file), user selectable
WAV file stimulusSoundCheck can use any WAV file as a stimulus. This enables the use of speech or music for realistic testing. If you want to use a custom signal that you cannot create using SoundCheck’s stimulus editor, it can be made in another program and saved as a WAV file for use in SoundCheck. SoundCheck offers active speech level control (required for some telephony standards) in the stimulus editor (requires active speech module p/n 2033)
Composite stimuli can be created using the stimulus editor. These are useful for tests that require a conditioning signal to warm up the device or open up a speech activity detector before playing the stimulus signal. SoundCheck also offers the ability to accurately analyze the response to composite source signals as it can be set to ignore parts of the stimulus when doing the analysis.
See our white paper on stimulus signals – featuring images and sound files.