Boss SD-1

The second pedal to be analyzed will be the Boss SD-1 “Super Overdrive” guitar effect. It is the longest produced pedal still being made by Boss, released in 1981. It is known for it’s ability to push a tube amp or other guitar pedals into overdrive with it’s boosted midrange, and is a direct competitor to the Ibanez “Tube Screamer”. Boss likes to advertise it’s “asymmetrical clipping”.

For this test, we will be using the 40th anniversary version of pedal.

EQ

Tone @ Min

Tone @ 12:00

Tone @ Max

We can quickly see why the pedal is well known for it’s midrange focused sound; every setting of the tone knob results in a significant midrange boost. The main effect of the tone knob is placing the mid range boost. All settings involve a fair amount of high and low frequencies being rolled off, leaving a wide bandwidth mid boost.

• With the tone at minimum, we can see a mid peak around 500Hz.

• With the tone at 12:00, we can see a mid peak around 1000Hz.

• With the tone at maximum, we can see a mid peak around 1500Hz.

The EQ curve is very similar to the Ibanez Tube Screamer. In the next sections, however, we will see that the SD-1 is not quite the same as a tube screamer.

Overtones

Drive @ Min

Drive @ 12:00

Drive @ Max

The SD-1’s overtones show us a lot about the gain range and feel of the pedal.

• At minimum drive settings, there is very light clipping happening, but more than the BD-2. This means that the pedal can’t be used as a purely clean boost with EQ shaping, although it comes close. It is worth noting that the SD-1 can’t boost overall volume at minimum drive settings, and actually loses some volume unless some overdrive/overtones are introduced.

• At 12:00 drive settings, we see a lot more overtones are produced. It is worth noting that there are even interval harmonics created, which is the main observable difference between this pedal and the Ibanez Tube Screamer. Stronger even harmonics are present in sawtooth waves, and often fuzzes and sometimes distortion pedals. The main affect of these even harmonics is extra overtones, most noticeably the added overtone exactly one octave above the fundamental note. This is NOT present with a Tube Screamer.

• At maximum drive settings, there isn’t near as much change in overtones as the first half of the gain knob. Unlike the BD-2, the gain doesn’t keep increasing until the pedal can be used for heavily saturated distortion/fuzz like tones. The largest effect of having the gain this high would be more compression due to overtones being produced more prominently as the input volume falls while notes sustain.

Waveform

Drive @ Min

Drive @ 12:00

Drive @ Max

The SD-1 waveform is interesting to at because we can see the asymmetrical clipping that Boss promotes.

• At minimum drive settings, the waveform is virtually unchanged.

• At 12:00 drive settings, we see the waveform begin to look like a softened square wave. We can also see that the top half of the waveform has both a higher amplitude (taller) than the bottom half, and a slightly different shape. This is what Boss is referencing when they mention asymmetrical clipping, and is possibly what is responsible for those additional even order harmonics/overtones seen in the previous section.

• At maximum drive settings, we can see what we saw in the overtones section; the wave shape doesn’t change much like it did in the first half of the drive knob’s range.