Hi all,
The built-in microphone on my DH-IPC-PT2849C1-S-PV-PRO has an interference problem that I've traced to its source. Dahua support says it's within spec, so I'm posting to see if anyone else has the same issue or a workaround.
Camera:
THE PROBLEM
1. Chirping. There's a rhythmic, cricket-like chirp in the audio, 24/7. It appears when IVS or SMD 3.0 is enabled and stops as soon as both are disabled. It's repeatable, with all other settings unchanged.
2. Noise Filter. The built-in Noise Filter does reduce the chirp and the hiss, but at every level it also cuts out speech: words, parts of sentences, even shouting. That makes it unusable.
WHAT I'VE RULED OUT
SPECTRAL ANALYSIS (recording with IVS on)
Nothing outside the camera can be phase-locked to its frame clock, so the interference is generated inside the camera. Most likely the analytics load couples into the mic path.
With IVS/SMD off, the loud bursts go away. A weak 20 Hz-locked ripple stays in the same band (modulation depth about 9%, versus about 19% with analytics on), along with a constant tone at about 4086 Hz.
DAHUA'S ANSWER
Support forwarded my report to the product team. Their reply: "they have to amplify the audio using very high levels before they can hear anything. Their conclusion is for this level to be within specifications for this product model."
I don't agree. At 40% sensitivity the chirp is clearly audible on normal playback (see the attached videos). "Within spec" also doesn't explain why the audio changes when IVS/SMD is switched on. And disabling the camera's main smart features isn't a fix.
Attached: two videos with uncompressed PCM audio, one with IVS/SMD on (chirping) and one with it off.
The built-in microphone on my DH-IPC-PT2849C1-S-PV-PRO has an interference problem that I've traced to its source. Dahua support says it's within spec, so I'm posting to see if anyone else has the same issue or a workaround.
Camera:
- Model: DH-IPC-PT2849C1-S-PV-PRO
- System version: V3.000.0000000.10.R, build date 2026-02-06
- Web version: V5.1.0.2403546
- Algorithm version: 1.0.6
- Audio: PCM, 16 kHz, mic sensitivity 40%
- Video: H.265, VBR, 4K @ 20 fps
THE PROBLEM
1. Chirping. There's a rhythmic, cricket-like chirp in the audio, 24/7. It appears when IVS or SMD 3.0 is enabled and stops as soon as both are disabled. It's repeatable, with all other settings unchanged.
2. Noise Filter. The built-in Noise Filter does reduce the chirp and the hiss, but at every level it also cuts out speech: words, parts of sentences, even shouting. That makes it unusable.
WHAT I'VE RULED OUT
- Cable / PoE extender: same chirp on an old 15 m direct PoE connection (the current install is 150 m with an extender).
- PoE power: same with a 12 V PoE splitter (camera on 12 V DC, no PoE on the port).
- Codec: same with AAC and PCM.
- Ferrites on the cable: no change.
- Environment: see the analysis below.
SPECTRAL ANALYSIS (recording with IVS on)
- The interference sits in 3.8-7 kHz, with nothing below 3.5 kHz. That's why it almost disappears at an 8 kHz sample rate.
- It comes as bursts of 20-30 ms, about 10 dB above the background in that band.
- The burst envelope is modulated at exactly 20.0 Hz and 40 Hz, which is the video frame rate (20 fps).
- The phase stays locked to the 50 ms frame grid for the whole 18 s recording: coherence 0.83, versus 0.42 or less for any other rate between 15 and 30 Hz. The 0.3-3 kHz band shows no such modulation.
Nothing outside the camera can be phase-locked to its frame clock, so the interference is generated inside the camera. Most likely the analytics load couples into the mic path.
With IVS/SMD off, the loud bursts go away. A weak 20 Hz-locked ripple stays in the same band (modulation depth about 9%, versus about 19% with analytics on), along with a constant tone at about 4086 Hz.
DAHUA'S ANSWER
Support forwarded my report to the product team. Their reply: "they have to amplify the audio using very high levels before they can hear anything. Their conclusion is for this level to be within specifications for this product model."
I don't agree. At 40% sensitivity the chirp is clearly audible on normal playback (see the attached videos). "Within spec" also doesn't explain why the audio changes when IVS/SMD is switched on. And disabling the camera's main smart features isn't a fix.
Attached: two videos with uncompressed PCM audio, one with IVS/SMD on (chirping) and one with it off.
