Spectrum analysis of the Electro-Harmonix Small Stone phase shifter
Ok, I just received my new soundcard so I just decided to run some tests on a Small Stone I borrowed.
Test setup
I used Cool Edit Pro to generate and loop a white noise signal, at -20dBFS. This plays only on the right channel of the soundcard, which is connected to the Small Stone input. The pedal output is hooked to the soundcard's left input, and this signal is analysed using Spectra Pro. The soundcard is an M-Audio Audiophile 2496.
The pedal was tested in it's slowest speed for the spectrum analysis. By the way, it is an original made in USA version, and seems very old.
Let the images speak
Click on the images to enlarge
The red line is the signal with the effect in bypass.
Minimum frequencies, no color
This is the lowest point in the sweep, reaching 119hz and 716hz.
Maximum frequencies, no color
The highest point in the sweep, reaching 716hz and 4360hz.
Minimum frequencies, color
This is the lowest point in the sweep with the color switch activated. It reachs 120hz and 800hz.
Maximum frequencies, color
The highest point in the sweep with the color switch activated. It reachs 1106hz and 6666hz.
Some conclusions
The ratio of the notches is roughly 6. That is, the high notch frequency is always 6 times the low notch frequency. This is a high 5th on musical terms. I always thougth this pedal sounded very "compact", maybe this is the reason?
The sweep in normal mode also has a ratio of six. That means, the frequency at the highest point of the sweep is 6 times the frequency at the lowest point, for both notches.
The sweep is extended when the color switch is engaged, and is rougly 9x. It goes about a 50% higher than in normal mode.
The deep of the notches varies around 35/45dB at different points of the sweep, counting from the bypass level.
It seems that there is some power lost when the effect is engaged, at least in normal mode, but I didn't noticed it when playing with the pedal thru the amp.
The color mode reinforces peaks between the notches (as expected), aproximately 10dB of gain. That's comparing with the base level with the color disengaged.
A view of the LFO
This is a shot using the 3d surface mode of Spectra Pro. It shows the spectra analysis across time, so you can see the actual variation the effect produces.
The graph is a little muddy, but I think the LFO shape can be seen without effort. It clearly shows the hypertriangular wave, with the tops rounded. I think it's interesting because it shows the actual frequency movement, which is a combination of the LFO shape and the transfer characteristic of the OTAs used for modulation.
Now I can't wait to put my hands on other phasers to compare!
Experiment #03
bioroids.miguelNOSPAM@yahoo.com.ar (Quitar NOSPAM) http://www.bioroids.com.ar