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Toneburst Test Signal CD
The audio signals on the CD allow you to test and evaluate the behavior of your listening room in response to your loudspeakers. At frequencies below 200 Hz the tests rely on listening and lead to the detection of room mode (resonance, standing wave) frequencies and their effect upon the reproduction of fluctuations in the low frequency multi-burst test signal.
Room reflections are best evaluated by using a storage oscilloscope to display the time
response to a short duration toneburst.
For other tests using the toneburst signals see the more detailed description of
the CD track contents below.
Ordering and payment information
These 28 files are available as download and to play from your computer's memory or to burn to CD-R. But CD-R
degenerate over time and become useless.
How to use the different sound tracks
The sound tracks on the CD are primarily for an analysis
of loudspeaker and room. The solution to any problems discovered could cover a
wide range of options and is left up to your resourcefulness. It will rarely be
a case of moving the speakers just a few inches. Please do not ask me for free
advice, but study the Room Acoustics pages.
For example, a single resonance with a 60 dB decay time
T60 of 500 ms will have a rise time of
You will be able to hear the dominant resonances of your
room during the sweep and be able to determine their approximate frequency by
measuring the time from start of the sweep with a stop watch. For example, if a
noticeable peak in volume occurred 18 s after the start, then the frequency
would be 200 Hz - (18 s) x (5 Hz/s) = 110 Hz.
As an informative experiment download and play a 200 Hz
to 20 Hz sweep from Track 1 to test your loudspeaker and room combination for
boom and rattle. 200-20Hz_sweep.wav
Listening to the signal gives an averaged impression of room/speaker response. Room modes cannot build up to full strength, because frequency and amplitude of excitation are continuously changing at random. Real signals of interest, like music, are much more periodic. So this signal is the extreme opposite to the swept sine wave. But, rarely is music as static as a constant amplitude sine wave, which is another extreme case. Live sounds fall between the two test stimuli and are somewhat closer to the sine wave.
Tracks 3 - 5
Track 3 provides 20-cycle bursts at 200, 180, 160, 140,
120, 110, 100 Hz.
Listen for the amplitude fluctuation in each multi-burst
signal as its frequency changes. The degree of articulation changes depending on
the burst's proximity to room mode frequencies and from where you listen in the
room. The sound may drone without any articulation, as in the bottom trace
of the graph above, or even seem to fluctuate at a higher rate when multiple
modes interfere with each other. The goal is to hear consistent articulation
from the normal listening place. In that case you can expect to hear musical
sounds with high resolution and without muddying.
The frequency steps between bursts are relatively wide and these tracks are intended for a coarse investigation or for highly damped room which have a wide bandwidth for each mode.
Tracks 6 - 13
Track 6 provides 20-cycle bursts at 4 Hz frequency steps
from 200 Hz - 160 Hz.
The different tracks allow a high frequency resolution analysis of mode behavior, as described for tracks 3-5. Specific mode frequencies that were found with track 1 can be further investigated, but other frequencies should be listened to as well, because the stimulus signal is different. Special care must be taken with tracks 12-13 not to damage the woofer by excessive cone excursions. There is no danger of thermal damage, because the burst signal duration is short and of low duty cycle.
The signal is used to determine the presence and delay in arrival time of room reflections. It requires the use of an oscilloscope, preferably with digital storage. I am not aware of a test signal that allows for audible discrimination between direct and reflected sound. The path length difference between direct and reflected sound can be determined from the speed of sound, 343 m/s = 34.3 cm/ms or about 1 ft/ms, and the time differences measured with the oscilloscope. It becomes then a matter of finding in your room where the reflection occurs and whether it can be attenuated or diffused.
The short duration test burst allows about 20 cm resolution of distance. The signal is most likely radiated from the tweeter in your loudspeaker. Being of short duration and low duty cycle you can safely increase its level until you hear the beginning of a change in sound character, which indicates clipping of either the power amplifier or the tweeter. Reduce the level until you are in the linear operating range again.
Tracks 15 - 17
Track 15 - Four single bursts at 20, 24, 32, 40, 52, 64,
80, 100, 128, 160, 200 Hz.
In combination with a microphone and oscilloscope, a fast,
peak holding SPL meter or custom peak
detector, these test signals can be used to determine a meaningful in-room
response of your speaker that correlates well with perception. The Radio Shack
SPL meters are not suitable, because they respond too slowly.
The signal is intended for listening tests. Since it is a
dual mono sound you should listen for a stable center image from your stereo
speaker setup. Move away from the "sweet spot" to hear how well the
image holds up.
With a little practice and experience pink noise can become a very revealing test signal.
Track 19 12.8 kHz, 5 bursts, 1 s
The tracks were generated by using the Expression Evaluator f(x) in the GoldWave Digital Audio Editor. The 5-cycle burst is one envelope period of an amplitude modulated sinewave of frequency f. It is described by the expression:
One period was copied for each of the ten frequencies f from 25 Hz to 12.8 kHz, and then pasted 5 times into a New Sound file which had 5 s or 10 s length.
In a similar way you could generate most of the test waveforms for the other tracks described above. For example, the expression for a 4-cycle burst with Blackman envelope is:
1 - Siegfried Linkwitz, Investigation of Sound Quality Differences between Monopolar and Dipolar Woofers in Small Rooms, 105th AES Convention, San Francisco, 1998, Preprint 4786, Abstract, Manuscript
Pink Noise Imaging Tests
Pink noise is a test signal for which the evolutionary brain has no natural equivalent. It is not clear what it is supposed to sound like. The closest might be the breaking ocean surf. Pink noise is very useful for pointing out differences between left and right speakers due to room setup or component variations. It can be very difficult, though, to track down the cause of the sonic differences. Two different pairs of loudspeakers will almost certainly sound different, but that does not translate proportionally to program material. It depends highly on the spectral content of the program material.
A stereo system should be able to create a solid center phantom image on mono pink noise and produce pitch changes due to comb filtering with lateral head movement. These pitch changes do not occur on program material of familiar sounds since the brain filters them out. Stereo pink noise should be smoothly diffuse and not change timbre when listening from different places in the room. I have generated a one minute test track that alternates between mono and stereo pink noise in 5 second intervals. You can check the center image for different room locations and setups. I added three 3 kHz and three 300 Hz ten-cycle shaped bursts at the end of the track to check the center image location and definition for click-like signals at those frequencies. The 3 kHz test result is very room reflection dependent.
Download and save pink-alternating3.wav (12 MB). Then burn the 1 minute sound file to a CD-R for convenient access and repeated play.
See also the Accurate Stereo page.
Toneburst Imaging Test
A rapid sequence of 22 tonebursts from 12.8 kHz down to 100 Hz can be used to check the spatial stability and focus of the stereo center image as a function of frequency. Each burst consists of 4-cycles of a sinewave with a raised cosine envelope. The sinewaves are at 1/3rd octave frequency intervals. The bursts are separated in time by 50 ms and room reflections can affect the phantom image location. The sequences are repeated 8-times going down and up in frequency.
The burst sweep can also be used to check for the onset of signal clipping as the playback volume is cautiously increased. The peak amplitude of each burst is constant at 0.9 FS.
Download and save 12_8k-100Hz-_4cycle_sweep_spaced_50ms_8x.wav (2 MB). Then burn the 12 second sound file to a CD-R for convenient access and repeated play.