--- Demo CD --- Toneburst
CD --- Music & sounds ---
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
Room reflections are best evaluated by using a storage oscilloscope to display the time
response to a short duration toneburst.
The response to short tonebursts from 20 Hz to 20 kHz can be
measured with a fast, peak holding SPL meter, if available, or a storage
oscilloscope. The Radio Shack sound level meters are too slow for the high
frequency bursts and at low frequencies their response is rolled off. Accurate
single burst measurements require instruments like the NTI
For other tests using the toneburst signals see the more detailed description of
the CD track contents below.
All signals are recorded equally in left and right channels. A voice
announcements of signal type and of each upcoming burst frequency is added to the
|1. 200Hz to 20Hz, 5 sweeps, 36s each, 5Hz/s rate, 3:18
2. 200Hz low-passed pink noise, 2:07
3. 200Hz to 100Hz, 3 bursts of 4x 20-cycles, large steps, 0:55
4. 100Hz to 50Hz, 3 bursts of 4x 10-cycles, large steps, 0:54
5. 50Hz to 20Hz, 3 bursts of 4x 10-cycles, large steps, 1:09
6. 200Hz to 160Hz, 3 bursts of 4x 20-cycles, 4Hz steps, 1:27
7. 160Hz to 120Hz, 3 bursts of 4x 20-cycles, 4Hz steps, 1:31
8. 120Hz to 100Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:15
9. 100Hz to 80Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:13
10. 80Hz to 60Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:15
11. 60Hz to 40Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:17
12. 40Hz to 20Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:39
13. 20Hz to 10Hz, 3 bursts of 4x 10-cycles, 2Hz steps, 1:34
14. 4kHz, 4-cycle bursts at 100ms intervals, 3:09
15. 20Hz to 200Hz, 4 bursts of 4-cycles, 1/3rd oct steps, 1:54
16. 200Hz to 2kHz, 4 bursts of 4-cycles, 1/3rd oct steps, 1:47
17. 2kHz to 20kHz, 4 bursts of 4-cycles, 1/3rd oct steps, 1:52
18. 20kHz pink noise, 2:07
19-28. 12.8 kHz to 25 Hz in oct steps, five 5-cycle bursts each oct
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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.
Listen to the audio tracks from your "sweet spot",
but also from other places in your room. Move your head to note how quickly or
how slowly a phenomenon changes with position. Check what you find against any
theories and claims you have subscribed to. Direct experience is the ultimate
arbiter. The acoustic behavior of real rooms is exceedingly difficult to
The first 13 audio tracks are limited to frequencies below 200 Hz, because this
is the range of discrete modes in typical size domestic listening rooms. The
upper limit of this range is given by the Schroeder
A constant amplitude sine wave that is slowly swept from 200 Hz to 20 Hz at
a rate of 5 Hz/s. This rate is slow enough so that a typical room
resonance can build to nearly full amplitude.
For example, a single resonance with a 60 dB decay time
T60 of 500 ms will have a rise time of
Trise = 0.32 T60 = 160 ms.
During that time the swept frequency will have changed by
(0.16 s) x (5 Hz/s) = 0.8 Hz,
which is small in absolute terms and also small when compared to the -3 dB
of the resonance.
BW = 2.2 / T60 = 4.4 Hz
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.
You will probably also notice various buzzes and rattles at different
frequencies caused by objects in your listening room, or possibly by your
speaker itself. As the sweep approaches its low frequency end you may have to
reduce the volume level to avoid bottoming and possibly damaging the woofer. Be
careful with this test. Start out at low volume levels. Every speaker is
eventually limited by its cone excursion capability.
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
Start out at low volume level to avoid damage of the woofer from extreme
cone displacements. Use an elapsed time measurement to determine the worst room
resonance frequencies. A Real Time Analyzer (e.g. AudioTools application for
iPhone) is convenient to show approximate frequency and and amplitude values.
The amplitude can vary widely between different locations in the room.
Pink noise that is limited to frequencies below 200 Hz. The signal changes
randomly in amplitude and frequency. The magnitude of its spectrum envelope
decreases at 3 dB/octave (10 dB/dec) towards high frequencies. The noise
waveform, below, clearly shows a maximum rate of change of around 200 Hz, when
you visually compare it to a 200 Hz sine wave.
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
Multi-burst signals consisting of four consecutive 10-cycle or 20-cycle
bursts with cosine envelope as in the top trace of the graph below. This is
identical to four modulation rate cycles of a 100% amplitude modulated sine
wave. The modulation rate is 1/10th or 1/20th of the carrier frequency. Each
multi-burst signal is repeated three times.
Track 3 provides 20-cycle bursts at 200, 180, 160, 140,
120, 110, 100 Hz.
Track 4 provides 10 cycle bursts at 100, 90, 80, 70, 60, 55, 50 Hz.
Track 5 provides 10 cycle bursts at 50, 45, 40, 35, 30, 25, 20 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.
For more background on these and other room response tests see Ref.1 in Publications.
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
Multi-burst signals consisting of four consecutive 10-cycle or 20-cycle
bursts with cosine envelope. This is identical to four modulation rate cycles of
a 100% amplitude modulated sine wave. The modulation rate is 1/10th or 1/20th of
the carrier frequency. Each multi-burst signal is repeated three times.
Track 6 provides 20-cycle bursts at 4 Hz frequency steps
from 200 Hz - 160 Hz.
Track 7 provides 20-cycle bursts at 4 Hz frequency steps from 160 Hz - 120 Hz.
Track 8 provides 10-cycle bursts at 2 Hz frequency steps from 120 Hz - 100 Hz.
Track 9 provides 10-cycle bursts at 2 Hz frequency steps from 100 Hz - 80 Hz.
Track 10 provides 10-cycle bursts at 2 Hz frequency steps from 80 Hz - 60 Hz.
Track 11 provides 10-cycle bursts at 2 Hz frequency steps from 60 Hz - 40 Hz.
Track 12 provides 10-cycle bursts at 2 Hz frequency steps from 40 Hz - 20 Hz.
Track 13 provides 10-cycle bursts at 2 Hz frequency steps from 20 Hz - 10 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.
A 4-cycle toneburst of 4 kHz frequency with Blackman envelope. It is
repeated at 100 ms intervals, which is a 10 Hz rate.
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
A 4-cycle toneburst with Blackman envelope that is repeated four times at
each frequency. The burst covers a spectrum of about 1/3rd octave around its
frequency. The Blackman time envelope was chosen for better attenuation of the
spectral envelope at low and high frequencies than obtainable with a cosine time
window. The burst frequencies are at approximately 1/3rd octave steps.
Track 15 - Four single bursts at 20, 24, 32, 40, 52, 64,
80, 100, 128, 160, 200 Hz.
Track 16 - Four single bursts at 200, 240, 320, 400, 520, 640, 800, 1000, 1280,
1600, 2000 Hz.
Track 17 - Four single bursts at 2, 2.4, 3.2, 4, 5.2, 6.4, 8, 10, 12.8, 16, 20
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.
By observing the envelope decay of the burst on an oscilloscope you can see
resonant decays that may be hidden in steady-state frequency response
measurement curves. For more details see Ref.13 in Publications.
These are also safe test signals to determine the maximum SPL levels that can be
obtained from a given power amplifier and/or loudspeaker at different
frequencies. The onset of distortion is clearly audible. Little heat is
generated in the voice coil, because the bursts have short duration.
Full bandwidth pink noise. The signal changes
randomly in amplitude and frequency. The magnitude of its spectrum envelope
decreases at 3 dB/octave (10 dB/dec) towards high frequencies.
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.
Move around in your room to hear changes in spectral balance due to the
directivity of your speakers. Move up and down.
Check the integration of drivers and seamless transition between their frequency
ranges by turning one ear to the speaker and moving up and down while about 1 ft
away from the front panel.
Compare left and right speakers by switching the noise between left and right
channels. The speakers must be placed right next to each other to avoid
influence of the room on the comparison.
Compare different speakers and listen for differences in tonal coloration.
With a little practice and experience pink noise can
become a very revealing test signal.
These tracks are useful for testing the onset of clipping in an audio
system. Each track contains five cosine-envelope or Hanning windowed bursts which were recorded at full
scale. The bursts are repeated at 1 s intervals from 12.8 kHz to 800 Hz and at 2
s intervals from 400 Hz to 25 Hz. Listen for the burst becoming distorted as the
volume level is increased. This indicates clipping in the electronics or a loudspeaker driver. It is a safe test when you increase the volume level
gradually until you hear distortion and then reduce the level immediately.
You can also use these tracks to listen for room reflections.
Track 19 12.8 kHz, 5 bursts, 1 s
Track 20 6.4 kHz
Track 21 3.2 kHz
Track 22 1.6 kHz
Track 23 800 Hz
Track 24 400 Hz, 5 bursts, 2 s interval
Track 25 200 Hz
Track 26 100 Hz
Track 27 50 Hz
Track 28 25 Hz
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,
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 file to a CD-R for convenient access and repetition of
the 1 minute sound file.
|| Stereo = L & R
|| Left = L
|| Right = R
|| Mono = L = R
|| 3 Bursts, 10 cycles @ 3 kHz,
-3 dB FS
|| 3 Bursts, 10 cycles @ 300
Hz, -3 dB FS
See also the Accurate