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Effects bypass comparison
While measuring the bypass properties of my PodXT, I took the opportunity to measure a few other devices. The selection of charts below shows how the bypass properties of a variety of effects units differ, including true bypass, FET-switched, buffered bypass and other DSP multi-fx units. Click here to return to the main PodXT page.
DSP Multi-fx Units
Let's start off with a quick reminder of the PodXT's bypass frequency response and a look at some other multi-fx units because they should be in the same ball-park as the PodXT (all these units have been set to their respective 'bypass' settings or at least had all the effects turned off).
Line 6 PodXT:
OK, the RP200A struggles a bit with keeping a flat EQ and also drops off at a lower frequency than the PodXT. The Pandora PX4 also drops off sooner than the PodXT. No real surprise here, both units are significantly cheaper than the PodXT so presumably compromises have been made. The last device, the Boss ME-50, is the best of the bunch with a cutoff frequency above 20 kHz. Again, no real surprise here as this is what the ME-50 is designed for - it's a high quality multi-effects unit designed to sit in between you guitar and amp so should have very good bypass performance. Also good to see the Zoom GFX-8 isn't far behind the ME-50's performance here.
True bypass and FET-switched pedals
OK, the next five charts are basically identical, have a look and then I'll explain my point below.
Marshall Bluesbreaker BB-2 Overdrive:
See how all the graphs are basically the same? Flat* frequency response all the way up and negligible latency (shown by the phase response). Well, the first two pedals (the Bluesbreaker and the Crybaby 535Q) are both 'true bypass' pedals. That means, when switched to bypass, the guitar signal runs straight from input to output, the only component it runs through is the switch itself. Some tone hounds maintain that true bypass is the only way to go. The alternative to true bypass is to use an electronic switch called a FET switch. Basically, the mechanical footswitch you step on is used to switch the electronic switch. It may sound a bit convoluted but, with a bit of extra circuitry the end result is a silent switch - no more loud pops when you step on the pedal. Nice. And the last three charts here (the Jekyll & Hyde, the Ibanez WD7 and the EH Holy Grail) are all FET-switched pedals. Any difference between true bypass and FET-switched throughput? No. Here's an interesting article on the subject.
* OK, there is a slight noisiness to these charts - ignore it, I just forgot to switch on averaging on the analyzer. Trust me, they're pretty much as flat as it gets...
Buffered bypass pedals and the Boss Loop Station
Now, I'm not sure about the comment in the article above about most pedals being buffered these day, especially in light of the above results, but I've seen the schematics of a few Boss pedals and they at least do have buffered outputs. So, let's grab a couple of Boss pedals and look at their bypass characteristics.
Boss PH-2 Super Phaser:
OK, the Super Phaser shows a little bit more loss than the previous set of pedals (around 1.5 dB). I can't really say the same for the Loop Station as it has adjustable input and output levels so this could be tweaked up a bit. Both, however, do show a little bit of tail off on the frequency response. The important thing to note here is that, as well as being only a slight change, the tail off is above 20 kHz. So, the buffer can have an effect on the tone, but Boss have tailored their buffer to only affect the signal beyond the audible range.
At first, the Loop Station's chart was a surprise to me. Because it's a digital recorder I'd assumed that its output would be similar to the DSP units and that having it in my effects chain would possibly be at some slight detriment to the guitar signal. But its output characteristics are basically identical to the Super Phaser. Then it clicked. Have a look at the two charts below which were taken with the Loop Station in playback mode:
Boss RC-20L Loop Station (playback 1):
Now, these charts might look rubbish compared to the charts from the DSP units above but that's down to the Loop Station's recorded test signal being significantly out of phase with the source signal from the analyzer. Remember that the Loop Station outputs both the recorded test signal in a loop and also the live test signal at the same time. The two charts were taken on separate record/playback runs and you see there are significant differences - it's really a timing/synchronisation issue, more down to my method of measurement than any fault of the Loop Station. The interesting thing here is that these charts show the recorded output is from a digital processor - see what happens around 17 kHz. That's the upper limit of the recorded signal but the live signal carries on through the Loop Station unaffected (see how, above 17 kHz, it matches the standard Boss bypass response). So, any digital compromises in the Loop Station are made only on the recorded signal being played back as a loop, the live signal through the Loop Station is treated just the same as any other Boss bypass.
A typical effects pedal chain
Lastly, here's a look at a relatively small chain of effects pedals in bypass. Here we've got the Jekyll & Hyde overdrive, the WD7 wah, the PH-2 Super Phaser, the EH Holy Grail reverb and finally the Boss Loop Station.
Effects chain:
No big surprises here. There's a fairly uniform loss (about 3 dB) throughout the audible frequency range and then the output starts to tail off near 20 kHz due to the buffered Boss pedals being there.