Noise in recordings

I am using Audacity 2.1.1 with Mac mini running OS X 10.9.5. It is a late 2012 with 2.3GHz Intel quad core I7 and 8Ghz ram. I record in the field with a Fostex flash card recorded, mostly 44.1 - 24 bit. I dump the recording from the Fostex into the computer, import it to Audacity, edit, and then export to desktop to burn to disc. This works perfectly. No noise problems. However, I also have reel to reel archive recordings to transfer to CD, which need to be edited. These I play from an Ampex ATR 100 into an Allen & Heath mixer, where I can control level and do EQ if necessary. The output of the mixer feeds the analog inputs of a Universal Audio Apollo Twin digital interface, which gets it into the Mac mini via a Thunderbolt connection, and the Audacity program for editing. Audacity is put into record, and the tape rolls. When the tape is done, I start to edit. The first 15 to 20 minutes will be perfect, but sometime in that 15 to 20 minute time frame, static noise begins to creep in, and as the program proceeds to it’s conclusion, the noise gets worse. It seems to be modulated somewhat by the audio. If it is someone talking, it is worse during the words, and quieter during the pauses between words or sentences. If it’s music, the louder it gets, the more static noise. The noise does not seem to have low frequency content, but is of a higher frequency nature. It is not clipping, as the audio level on the meters is running between -20 and -12. If I take the same tape recording, feed it into the Fostex, and then dump it into the computer, import it into Audacity and edit it, it will be perfect… NO NOISE. What am I doing wrong???

Mac mini via a Thunderbolt connection…What am I doing wrong???


That’s the same vintage machine as mine. I rather like the analog connections (I know this is the MacBook Pro illustration).

Unlike many Windows machines, the Mac analog connection is top quality. I shot all my client deliverables using the stereo analog-in connection and see no reason to stop.

The Thunderbolt adapters are not a gift from the angels. Someone did an analysis that the video adapter has a tiny processor and actually downrezzes the picture before you see it.

Not a fan.


In some cases, the Audacity Buffer setting can be changed to help strange audio noises.

Audacity > Preferences > Recording > Audio…Buffers.