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Old 16th December 2011, 08:29 AM
dalcocer Offline
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Location: San Diego, CA
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F16 Crackling noise in captured audio

I cannot produce a clean audio capture using Fedora 16 on my desktop PC. The captured audio has a faint but very noticeable crackling to it. Opening the captured audio file in Audacity shows clicks and pops in the recording.

Before I give up and install Windows 7, I thought I'd check here first to see if anything can be done to fix this.

I've verified the following:
  • there's no problem with the input audio cable (the same cable produces clean recordings with my laptop, using the Windows XP port of Audacity)
  • checked that I'm using the line input, not the microphone input
  • checked line input is unamplified (Applications, System Setting, Sound, Input tab)
  • audio output works fine (tested using known-good MP3 audio files)

I've attached the captured audio (dtmf-recording.zip) and the source audio (dtmf-sample.zip); both are FLAC files. The audio I'm using for testing is a small 12-second sample of eight DTMF tones; this input makes it easier to hear the distortion present in the captured audio.

Hardware: Asus Crosshair IV Formula motherboard (8GB RAM), using AMD Phenom II X6 1090T CPU (3.7 GHz).

Output of "sudo arecord -l"
Code:
**** List of CAPTURE Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: VT2020 Analog [VT2020 Analog]
  Subdevices: 2/2
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
Output of "sudo aplay -l"
Code:
**** List of PLAYBACK Hardware Devices ****
card 0: SB [HDA ATI SB], device 0: VT2020 Analog [VT2020 Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 1: VT2020 Digital [VT2020 Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: SB [HDA ATI SB], device 2: VT2020 HP [VT2020 HP]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
Output of "lspci -v | grep -A7 -i audio"
Code:
00:14.2 Audio device: ATI Technologies Inc SBx00 Azalia (Intel HDA) (rev 40)
	Subsystem: ASUSTeK Computer Inc. M4A89GTD PRO/USB3 Motherboard
	Flags: bus master, slow devsel, latency 64, IRQ 16
	Memory at fcbf8000 (64-bit, non-prefetchable) [size=16K]
	Capabilities: <access denied>
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd-hda-intel

--
06:00.1 Audio device: nVidia Corporation HDMI Audio stub (rev a1)
	Subsystem: eVga.com. Corp. Device 1521
	Flags: bus master, fast devsel, latency 0, IRQ 25
	Memory at fe97c000 (32-bit, non-prefetchable) [size=16K]
	Capabilities: <access denied>
	Kernel driver in use: snd_hda_intel
	Kernel modules: snd-hda-intel
Any ideas on how to fix this, or additional troubleshooting steps I should perform, are welcome.
Attached Files
File Type: zip dtmf-sample.zip (468.1 KB, 63 views)
File Type: zip dtmf-recording.zip (846.5 KB, 66 views)

Last edited by dalcocer; 16th December 2011 at 08:32 AM.
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  #2  
Old 16th December 2011, 05:56 PM
sonoran Offline
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Location: Sonoran Desert
Posts: 2,392
linuxfirefox
Re: F16 Crackling noise in captured audio

You've probably thought of this already, but make sure you mute your mic inputs.
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Old 16th December 2011, 10:19 PM
Chilly Willy Offline
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Posts: 1,258
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Re: F16 Crackling noise in captured audio

Since you say you are using an MP3 file, I'll assume that you are using an MP3 player for your input. If so, did you check that the output of this is clean? (or whatever device you ARE using?)

Just for "S & G's" what does it do if you DO use a mic? - what does Audacity's waveform look like then?
You may want to try something with a LOW output in the MIC input (other than the MIC) to see it it may be your line-in that is causing this. - make sure it matches the input requirement as not to damage anything. (low input amplitude & proper impedance - apm. being more important, for this short duration test)
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Last edited by Chilly Willy; 16th December 2011 at 10:21 PM.
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