constant hiss in screencast

[jollyfellow]

Hi I get a constant hiss with both the Linux screencast programs I've tried. I assumed this was to do with my microphone, so I've unplugged it, but I still get the hiss on playback. I also get a pop noise at the very start (and often at the very end) of my screencast videos. (Not the sound of me clicking the mouse!)

I've tried Kazam and RecordMyDesktop. An example is attached -the microphone is not plugged in.

I hope I'm not missing something obvious. Thanks for any thoughts.

[jollyfellow]

Whoops, apologies, should have posted this in the newbie section.

[jagabo]

The click comes from the strong DC offset when you start recording.



Note how the average level jumps from 0 to 0.7 volts. That's probably from bad grounding somewhere. The noise may come from that too. How high is the mic gain turned up?

[Cornucopia]

Not sure which input it is actually using, but sounds (pardon the pun) like you have a live input with nothing attached to it that some element of the software is applying AGC to, which would normalize the hiss. Then, because you hiss level is elevated, the standard start/end points, which have likely captured midpoint somewhere in a sample cycle, would exhibit a pop/click. The way to get rid of this is to edit using a software that cuts at the sample's zero-crossover point, or by applying fadeups and fadedowns.

Scott

[jollyfellow]

Not sure which input it is actually using, but sounds (pardon the pun) like you have a live input with nothing attached to it that some element of the software is applying AGC to, which would normalize the hiss. Then, because you hiss level is elevated, the standard start/end points, which have likely captured midpoint somewhere in a sample cycle, would exhibit a pop/click. The way to get rid of this is to edit using a software that cuts at the sample's zero-crossover point, or by applying fadeups and fadedowns.

Scott

er, as noted, I should have posted in the newbie section. Do you mean I ought to use something to remove the hiss after the fact? i've seen Audacity recommended, but obviously I'd rather not have to do any post processing.

[jollyfellow]

The click comes from the strong DC offset when you start recording.


[Attachment 18898 - Click to enlarge]

Note how the average level jumps from 0 to 0.7 volts. That's probably from bad grounding somewhere. The noise may come from that too. How high is the mic gain turned up?

I have no mic plugged in.

Bad grounding -do I need to do something to my laptop? Perhaps it's a power supply issue or the like? (I know very little about hardware)

[jagabo]

Running without the external power supply is worth a try.

When you do have the mic plugged in -- how high is your voice level? Is it totally blown out? If so, just turning the gain down may reduce the noise and the DC offset to bearable levels.

Or your laptop may just have a very poor audio section.

[jollyfellow]

Running without the external power supply is worth a try.

When you do have the mic plugged in -- how high is your voice level? Is it totally blown out? If so, just turning the gain down may reduce the noise and the DC offset to bearable levels.

Or your laptop may just have a very poor audio section.

I unplugged the power adapter at the plug socket, unfortunately this made no difference. I dare not actually unplug the power cable from the laptop because it's very temperamental -unplugging could mean 30 mins of getting it at exactly the right rotation so it works again!

With the mic plugged in, voice level on playback seems just about right. I lowered the input level in ubuntu sound properties, which reduced the hiss, but also reduced the volume of my voice to a similar degree. Unfortunately I need zero hiss and pops.

I also have a Windows 7 machine and tried camstudio.org. I got no hiss or pops, but even after experimenting with the audio options, the voice quality on playback was awful (which is not a problem with what I've tried on ubuntu, and I'm using the same microphone). tbh I'd really rather use my ubuntu machine anyway (for which I don't have a Windows install).

Do you think my best option is to accept that the hiss and pops will happen and try and remove them with Audacity or the like?

[jagabo]

Do you think my best option is to accept that the hiss and pops will happen and try and remove them with Audacity or the like?

No. Your best option is to get a quality external USB audio capture device with a mic input.

[jollyfellow]

Do you think my best option is to accept that the hiss and pops will happen and try and remove them with Audacity or the like?

No. Your best option is to get a quality external USB audio capture device with a mic input.

I was assuming that because the hiss happens even when no microphone is plugged in then the hiss will always happen, regardless of the kind of mic I have. Is this incorrect?

quality external USB audio capture device with a mic input

Would something like this USB mic do the job?

Sorry about the newbness of questions!

[jagabo]

I agree a different mic plugged into your laptop's mic input won't work any better. The Snowball should be fine. The A/D conversion happens in the mic so whatever's causing the noise in your laptop will be bypassed.

[jollyfellow]

I agree a different mic plugged into your laptop's mic input won't work any better. The Snowball should be fine. The A/D conversion happens in the mic so whatever's causing the noise in your laptop will be bypassed.

Thanks for the advice, I'll give that a try.

[jagabo]

Please write back and let us know how the Snowball worked for you.

[budwzr]

...Your best option is to get a quality external USB audio capture device with a mic input.

I'm looking for one of these too. Any suggestion? Don't need XLR.

[jollyfellow]

Please write back and let us know how the Snowball worked for you.

Will do. I need a set up good enough for professional level screencasting, so I'm wondering whether I need something more expensive, like this more expensive Blue one or this Audio-Technica -I'm on a tight budget so will probably dither for a while!

[jagabo]

I'm not an expert on microphones. But in my experience proper usage is more critical than exactly which mic you use (once you get beyond total crap mics). You want the mic to be as close as possible to the person speaking. Don't place the mic directly in front of the speaker's mouth unless you are using a pop shield. Don't place the microphone on the desk if you're going to be typing (or put the keyboard elsewhere) -- vibrations and noise from the typing will feed into the mic. You don't want the room to be too reverberant or too dead. Eliminate other sources of noise (computer, air conditioning, etc.).

[jollyfellow]

I'm not an expert on microphones. But in my experience proper usage is more critical than exactly which mic you use (once you get beyond total crap mics). You want the mic to be as close as possible to the person speaking. Don't place the mic directly in front of the speaker's mouth unless you are using a pop shield. Don't place the microphone on the desk if you're going to be typing (or put the keyboard elsewhere) -- vibrations and noise from the typing will feed into the mic. You don't want the room to be too reverberant or too dead. Eliminate other sources of noise (computer, air conditioning, etc.).

Great, thanks for the tips. I'm not sure how I'll avoid placing the mic on the desk while I type -sounds a little crazy but as a budget option I might try suspending it from the ceiling -a hook and a bit of string! Or failing that perhaps Blue's shockmount might do the job. Other than that I have no air conditioning, my Windows machine is pretty quiet and I've a generally fairly quiet environment, so hopefully I'm almost there.