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Experiments with sensitive IEMs


Jan 14, 2021

In the last year or so I've bought a few pairs of cheap IEMs, most recently the KZ ZS 10 Pros. I've noticed something that has made me curious.

I listen to music fairly quietly. In quiet tracks I can often hear a kind of distortion. The best way I can describe it is, it sounds like a "squiggle" and can be best heard during fade ins/outs and the beginning/end tracks. It's most noticeable when the source device is at low volume and at extremely low volumes the sound is almost grainy. Turning it up eliminates this, but can make it too loud to listen to. Note that it's not a hiss. Not like a noise floor (I hear noise floor too, but this is different).

Initially I had wondered if it was quantisation noise, but now I don't think so. Read on...

I tried some low-volume experiments with different devices to try to understand:

- Nokia 5.4 built-in DAC: noise floor audible, squiggle audible.
- Nokia 5.4 + Hidisz S9: noise floor inaudible, squiggle very pronounced.
- PC + Loxjie D30: noise floor very noticeable, but no squiggle.

I don't notice either the noise floor or the squiggle using over-ear headphones, which I assume are less sensitive.

At best that suggests that the squiggle and the noise floor are independent. Hrm...

Then I noticed that if I put an analog headphone amplifier (it's the Liam and Daan one) inline between the above source and the IEMS, turn the source up a lot, and use the amp to attenuate the signal to comfortable listening volume, both noise floor and the squiggle are gone. It's so much cleaner and more enjoyable.

So what's going on here? What the proper name for the "squiggle"? And am I not using the amp as the world's most inefficient potentiometer at this point? Could I achieve the same using a passive device (and is it called "a resistor" :p)?


EDIT: Just found the iFi Ear Buddy and IEMatch by searching for "headphone attenuator" on Amazon. Sounds like it's a known issue. Still keen to know if it's just a resistor so that I can maybe make one.

EDIT AGAIN: ah ha!
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