Audio recordings recorded through iNaturalist

General
1

I am trying to help on the ID of this insect https://www.inaturalist.org/observations/308982573

I have downloaded the audio file (1615393.m4a) which was recorded in iNaturalist on an iPhone 12 Pro and I’ve put the recording into audacity and I get the following information - where there doesn’t appear to be any frequencies much above 7000Hz

example
example1079×628 211 KB

I’m not familiar with recording sound with iNaturalist (or using an iPhone) and am wondering if the sound is modified by the app or the frequency range here is more likely to be due to the phone settings.

Thanks in advance

Pual

2

Phones are designed to transmit voice, and flapping folds of flesh form few formidable frequencies. I have a Sunlan recorder and just opened the latest file in Audacity; the sample rate is 16 kHz. What’s the sample rate on the one you listened to?

44100 Hz is a common sample rate for human-perceptible audio, but you’d want even higher if you were recording bats.

3

If you amplify the recording and filter a band between 6 and 8 kHz, and listen to the recording at 0’1x speed you can hear a distant stridulation.

4

Thanks phma

It isn’t my recording so I’m afraid it’s not my phone and I don’t know the sample rate used or the limitations of the phone in question (an iPhone Pro 12) but looking at the frequency diagram I think that the sample rate could be 16kHz as that would only record sounds up to 8Khz.

5

Thanks rafael - I’ll give it a go.

6

i don’t have an iPhone and i haven’t used the new app, but it seems like historically, the iNat apps have just piggybacked on the phone’s default camera and audio recorder. Apple is reputed to have a very good audio encoder, but without having access to the the original file on the device, it’s hard to say whether the possible cutoff in higher frequencies was present in the original recording.

it is known that when an M4A file is uploaded to iNat, the server reencodes it, and that is a point where audio problems also could be introduced. see https://forum.inaturalist.org/t/issues-with-quality-of-sound-recordings/52178/22.

7

Thanks very much pisum - I can see a lot of posts in that thread that will be useful.