Frequency Response measurements

Frequency Response measurements


Frequency Response can be obtained by analyzing the Impulse Response.


Impulse Response of the Loudspeaker


The Impulse must be windowed in order to analyze the anechoic part of the wave.


Frequencies computed by applying FFT to the above Impulse (far field measurement)



Above spectrum in 1/3 Octave bands

This window shows spectrum data computed from the selection in the Impulse (between the two cursors).

These measurements can be easily performed by using Sample Champion. Spectrum data (obtained by using the Fast Fourier Transform on the Impulse Response) can be analyzed in narrow-band or octave bands.

Frequency Response topics on this subject on PureBits site.

Go to Sample Champion features.


What is Sample Champion?

Accurate, fast and powerful

Sample Champion is an accurate and easy to use audio measurement software. It has been designed for acoustical technicians, sound engineers, scientists and students. With this software you'll be able to easily perform Impulse Response measurements, FFT analysis and much more.

Amazing features

Some very useful options are available, such as:

MLS(*) pre-filtering (pink and/or custom spectrum)
averaging in time and frequency domain
double precision FFT
real-time results (the Impulse Response can be monitored during the averaging process)

possibility to calibrate the system using internal or external sources

(*)MLS is an abbreviation for Maximum Length Sequence. It is basically a pseudo-random sequence of pulses. Nowadays MLS measurements are quite standard in many different application fields. One of them is acoustics.
More information about the measurement method used in Sample Champion can be found here.
More information and references about MLS measurement theory can be found in the bibliography section of this site.

Expandable and versatile

Sample Champion has been designed with special attention to the possibility of future improvements and expansions. Special purpose signal processing plug-ins are available and others will be released.


Currently available pugins:

Audio Quality Plugin
SNR (Signal to Noise Ratio)
THD and THD+N (Total Harmonic distortion)
IMD (Intermodulation Distortion)
Read more about this plugin in the Application note #8.
Go to Application notes main page: click here.

Filter Banks
This module allows to approximate BUTTERWORTH and CHEBYSHEV low-pass, band-pass and high-pass analog filters by means of IIR (Infinite Impulse Response) digital filters. Moreover two banks of IEC 1260 Octave and 1/3 Octave Filter Banks are implemented as presets. This module can be used for filtering a measured or loaded impulse response.
Read more about this plugin in the Application note #9.
Go to Application notes main page: click here.

Waterfall Plot
This module computes and plots (see the below figure) a 3D Cumulative Spectral Decay of an impulse response. This is an invaluable information for finding loudspeaker and box resonances. Many options are available, such as different FFT sizes and weighting windows (independently from the main program settings). Unreliable computed low frequencies are automatically rejected from the plot.
Read more about this plugin in the Application note #10.
Go to Application notes main page: click here.

Room Acoustics
This module computes and plots many acousical parameters, such as Reverberation Time, Early Decay Time, Definition, Clarity and Centre Time. Many options and features are available: the acoustical parameters can be computed in wideband or in octave or 1/3 octave bands. Results are available in tabular or graphic form. Time data can be plotted in many modes: Log Squared, Schroeder Plot, Step Response, Cumulative Energy. Inverse Schroeder Integration can take advantage of an user selectable noise compensation. Computed data can be exported to Clipboard and plots can be saved to disk as Bitmap images.
Read more about this plugin in the Application notes #11, 12, 13 and 14.
Go to Application notes main page: click here.

Go to Sample Champion features or go directly to the download page and try yourself the trial version of Sample Champion! (Sample Champion requires Windows 95/98/2000 or NT4 and a full-duplex audio sound card).

Sample Champion User Manual is now available as single printable PDF file . Click here.



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