Audio problem MacBook Air Project Rate 8000HZ

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lbalk
Posts: 2
Joined: Fri Dec 07, 2018 1:03 pm
Operating System: OS X 10.11 El Capitan or later (macOS)

Audio problem MacBook Air Project Rate 8000HZ

Post by lbalk » Fri Dec 07, 2018 1:22 pm

I am using a new Macboox Air, I use Audacity for phone system and voice mail greetings that must be recorded mono 8000Mhz and then exported to wav Ulaw.

When using my MacBook Pro I have no problem, when using the MacBook Air I can not use 8000 HZ for playback. I get static and noise using an internal or external microphone. I can record with no problem at 44100 HZ Mono, I can export it to a wav file open on a MacBook Pro and then save and export the file as 8000hz Ulaw with no problem. I get only noise and static on the MacBook Air when using 8000hz. Any suggestions or ideas on setting I may be missing.

Thank You

Leonard

steve
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Re: Audio problem MacBook Air Project Rate 8000HZ

Post by steve » Fri Dec 07, 2018 1:48 pm

lbalk wrote:
Fri Dec 07, 2018 1:22 pm
when using the MacBook Air I can not use 8000 HZ for playback
Sound cards generally support a small range of standard sample rates, but they do not always support the sample rates that they say they do.

What is supposed to happen if the sample rate that is played is not supported by the hardware is either:
1) If the sound card drivers support the sample rate, they will resample the audio to a supported rate on the fly, and pass the resampled audio to the audio hardware.
or
2) If the sound card drivers do not support the required sample rate, then Audacity will resample the data to a rate that is supported by the sound card drivers.

For (2) to work requires that the sound card drivers correctly report which sample rates they support. Some drivers don't do this correctly, so Audacity may think that a sample rate is supported when in fact it is not.

Te easiest workaround is to temporarily set the "Project Rate" (bottom left corner of the main Audacity window) to a sample rate that you know IS supported by the sound card - 44100 is a safe bet. This should allow tracks with any sample rate to play correctly in Audacity.

Note that the "Project Rate" sets the sample rate for exported files, so if you require a file that has a sample rate of 8000, then you must set the Project Rate to 8000 before you export.
9/10 questions are answered in the FREQUENTLY ASKED QUESTIONS (FAQ)

lbalk
Posts: 2
Joined: Fri Dec 07, 2018 1:03 pm
Operating System: OS X 10.11 El Capitan or later (macOS)

Re: Audio problem MacBook Air Project Rate 8000HZ

Post by lbalk » Fri Dec 07, 2018 5:15 pm

After reading this response, I recorded and edited the greeting using a higher sample rate. I then exported it with the sample rate I needed and played the file in iTunes successfully. I understood the response, I do not understand the full reason since the same file is played perfectly with another tool .

Leonard

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