micro-Thumpinator: I can't hear what it does, but it does what it should

[Ted]

Pedal Show-and-Tell...

I bought an SFX micro-Thumpinator for my bass. It's a "high pass filter" or a "bandwidth optimizer."

What it does is filters out infrasonic sounds – frequencies so low that people can't hear them, but they still rattle your amp (or headphones) and sap power from your mix. So it optimizes your sound for human hearing range.

Which is kind of a paradox: If it filters out sounds that I can't hear, how do I know if it's doing what it's supposed to do?

What it's supposed to do is filter out notes beginning at 25Hz  – which is the G#/Ab below the low open B on a 5-string bass, or an octave below the lowest B on a 4-string bass (A string, second fret). But the immediately neighborhood below the low B can start to sound like mush, even for humans.

30Hz is an octave below this note on a 4-string bass

I recorded a short thing with my 5-string (low B) bass running through an octave down effect (also a new toy), one time with the micro-Thumpinator, and again without. I made sure to hit the low B note a couple of times. So that octave down from the open B should be 15Hz, I reckon. (Elephants can hear that.) I recorded WAV files, so there would be no compression.

I opened these WAV files in Audacity and used the Frequency Analysis tool to look at what the micro-Thumpinator does.

Here are the results:

I put the cursor on 30Hz – just before where the micro-Thumpinator is intended to begin filtering.

So it works! I can't wait until the next time I get to plug into an amp and try the same test to see if the amp rattles less with the micro-Thumpinator engaged.

Here's what Max at SFX says about it:

The micro-Thumpinator is very useful in at least the following situations:

• Amplification through bass amplifier.
• Recording in a studio-grade audio interface.
• Filtering before compressors, envelope filters and other pedals that operate in relation to the signal amplitude.
• Post-octaver filtering. Especially, for digital octavers that don't have a post-wet filtering

Back in the USA, I have a bass amp in storage, with a built in octave effect, and I never liked the way it sounded. It had that mushy sound on the lower notes, but I didn't really think about why – infrasonics and such. I just knew I didn't like it as much as I wanted to like it. Then I heard of the micro-Thumpinator when I saw this rig rundown video for Dusty Hill's gear. And I said to myself, "This guy gets it" and "I want one of those."

Max is a great guy. He honored his "free shipping worldwide" promise, even to me in Madagascar, which definitely cut into his profit on this unit. And he has patiently answered all my fool questions.

Here's where you can get one.


PS: If you're wondering what all that noise is below 10Hz, I don't know, but I think it's just infrasonic noise added by the Micro BR, or maybe the noisy electricity here in Madagascar. In any case, I believe it's noise introduced after the micro-Thumpinator.

[Zoltan]

A great breakdown of infrasonics yet still goes over my head Is there something magical happening that can't be handled by EQ? (before, or after) Or is it just the ease of use?

AirWindows has some infrasonic filters in vst form ( https://www.airwindows.com/infrasonic/ ). Just thought to mention if needed.

[dasilvasings]

Really interesting. I frequently use high pass filter at around 20hz to "cut the mud". I usually do this in post production. For what I know, most EQ stompboxes can cut some 10db around 30hz, but that is not a clear high pass filter. There is some sort of Q shape related with the EQ.

Really curious about those low harmonics. I thought the electrical noise was 50/60 hz and its multiples, but I am not an expert. Was there any earthquake in Madagascar?   

But anyway, -78 dB is quite low... so I guess I can live in ignorance..

[Ted]

Is there something magical happening that can't be handled by EQ? (before, or after) Or is it just the ease of use?

I'm not an expert, but an equalizer will let you tweak frequencies within particular ranges represented by each slider. For example, a graphic equalizer may have three bands, or 31 bands. But it may not include a way to roll off all infrasonic frequencies below a particular threshold - which is what a high-pass filter does.

The main difference between filters and equalizers are that filters only attenuate (i.e. reduce) certain frequencies in the spectrum, whereas equalizers can either boost or attenuate the strength of particular frequency bands of the spectrum.

This video is a good demonstration of what the micro-Thumpinator does:

https://www.youtube.com/watch?v=TacaSl6dimU

My recording scenario is still mostly Micro-BR and GarageBand (without plug-ins). And I play live a few times a year. I have been wanting to add an octave-down effect in both scenarios, and I wanted to avoid the mushy bass sound that I experienced previously. Also: I'm a very reluctant/lazy tweaker; I use presets for equalizing, and mastering. The micro-Thumpinator is a very well-reviewed piece of gear, and it satisfies both of my playing scenarios and also my lazy streak.

[Ted]

Really curious about those low harmonics. I thought the electrical noise was 50/60 hz and its multiples, but I am not an expert. Was there any earthquake in Madagascar?   

I'm kind of curious about that too. If it's not just the noisy power here in Madagascar, it may be that the Micro-BR is not a "studio-grade audio interface."

If I really wanted to test this further, I would run the Micro BR on battery power, and plug the bass directly into the micro-Thumpinator, and output to the Micro BR. Then I would turn the volume knob on the bass all the way down. And I would record a few seconds of nothing at all, and then I would do the frequency analysis on the WAV file.

This sounds like exactly the type of curiosity-satisfying thing that I will do when I should be spending my time on creating music.