<p>Sometimes even if the device itself is good (quiet), the power source may be noisy. Ships are notorious for their power gremlins, even on 'quiet' power supplies. It is hard for a big metal ship to have a proper ground in the ocean (see dark magic comment!).  Over the years I have gone so far as to cut my cables to bypass the DC-AC converters &amp; power directly into batteries, use optically isolated serial port connectors and 'quiet' USB hubs (sorry, the devices I used are out of date so I cannot provide any links).</p>

CC BY-SA 4.0
2022-07-01T00:01:48.693Z
2022-07-01T00:01:48.693Z
Shannon
<p>AFAIK all consumer-grade DC-AC converters produce such multi-harmonic interference. I too had this issue, and even tried out multiple converter models with no luck.</p>
<p>Your best shot may be to use shielded cables for your mics, though here too i don't know if it will definitely work (if memory serves right, shielding didn't help here). The final alternative that worked for me was to ditch the converter+ soundcard combination and use another model that had DC power supply.</p>
<p>Also, the interference may be there on the audio, but aside from the cosmetic inconvenience - how much of it is there? It's worth quantifying the dBrms of audio recorded with/without the converter to assess if it really makes a big difference after all.</p>

CC BY-SA 4.0
2022-06-29T21:09:51.403Z
2022-06-29T21:09:51.403Z
Thejasvi
<p>I'm using a DC-AC converter to run my audio-interface in the field. Everytime I use the converter to make recordings i see strong multi-harmonic 'lines' in my spectrogram. In the lab (when connected to mains power) however, the lines do not appear.</p>
<p>I've tried various approaches including placing sound card far from the converter and even 'grounding' the converter with a metal rod connected to the box. The lines still appear. How can I ensure the interference doesn't happen?</p>

CC BY-SA 4.0
2022-07-01T01:52:22.227Z
Could you possible add an example spectrogram? I think I also deal with what you are describing but would love to compare
selene
CC BY-SA 4.0
2022-07-01T05:01:52.303Z
Don't know if i have it at hand any more. This was looong ago :|. This actually could be a separate question :)?!
Thejasvi
<recording><experiment-design><fieldwork>
how do I get rid of multi-harmonic lines in my recordings?
# how do I get rid of multi-harmonic lines in my recordings?

(Asked by: username_0 on 2022-06-29)

I'm using a DC-AC converter to run my audio-interface in the field. Everytime I use the converter to make recordings i see strong multi-harmonic 'lines' in my spectrogram. In the lab (when connected to mains power) however, the lines do not appear.

I've tried various approaches including placing sound card far from the converter and even 'grounding' the converter with a metal rod connected to the box. The lines still appear. How can I ensure the interference doesn't happen?

**Tags:** recording, experiment-design, fieldwork

> **Comments:**
> **username_1**: Could you possible add an example spectrogram? I think I also deal with what you are describing but would love to compare  
> **username_0**: Don't know if i have it at hand any more. This was looong ago :|. This actually could be a separate question :)?!  

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## 2 answers

### Answer by username_2 on 2022-07-01. Score: 3

Sometimes even if the device itself is good (quiet), the power source may be noisy. Ships are notorious for their power gremlins, even on 'quiet' power supplies. It is hard for a big metal ship to have a proper ground in the ocean (see dark magic comment!). Over the years I have gone so far as to cut my cables to bypass the DC-AC converters & power directly into batteries, use optically isolated serial port connectors and 'quiet' USB hubs (sorry, the devices I used are out of date so I cannot provide any links).


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### Answer by username_0 on 2022-06-29. Score: 3

AFAIK all consumer-grade DC-AC converters produce such multi-harmonic interference. I too had this issue, and even tried out multiple converter models with no luck.

Your best shot may be to use shielded cables for your mics, though here too i don't know if it will definitely work (if memory serves right, shielding didn't help here). The final alternative that worked for me was to ditch the converter+ soundcard combination and use another model that had DC power supply.

Also, the interference may be there on the audio, but aside from the cosmetic inconvenience - how much of it is there? It's worth quantifying the dBrms of audio recorded with/without the converter to assess if it really makes a big difference after all.


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