Rockbox General > Rockbox General Discussion

Can Rockbox make the iriver ihp-140 to work as a SPL meter?

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saratoga:
Have you looked at what is already included?  spectrogram, mono, integration are already available...

LADave:
Searching "spectrogram" doesn't turn up anything.  "fft" is slightly productive.  There seems to be a plug-in but I couldn't find anything about it in the half-dozen manuals I looked at.  There doesn't seem to be a mechanism for (globally) searching manuals comparable to searching forums.

VU meters are different from SPL meters.  For one thing, VUs are tied to gain vs. clipping levels whereas SPLMs are calibrated to absolute sound pressure; 0 dB = 20 micropascals.

It's difficult to say how RockBox's VU integration settings correspond to "fast" and "slow" integration on SPLMs.  Perhaps someone who has worked on this would know, but given my previous quibble that may be moot.

LADave:
iPhones 4 and later have MEMS microphones (I'm not sure whether the electret-to-MEMS switch actually came earlier).  Compared to electrets, MEMS microphones are fabricated as chiips to ultra-exact tolerances.  They tend to have flatter, smoother frequency response, plus better consistency in sensitivity (millivolts per pascal) from sample to sample and batch to batch, and change less with age and environmental variability.  This predictability lets iPhone SLM apps like SPLnFFT be pretty accurate without calibration to individual iPhones. 

If Rockboxes have electret mics they will need calibration for accurate results and calibration is a tough nut to crack.  Most (all?) Rockboxes lack the cylindrical microphone snouts that conventional meter calibrators attach to, and the average user is unlikely to have ready access to a calibrator anyhow.  The alternative method appears to be side-by-side calibration versus a known accurate SLM, preferably in a special room setup where sound levels don't vary over a few inches of separation.  Not many users have access to these either.

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