Noise during recording

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I am on mac os sierra 10.12.6, I use audacity version 2.1.0 installed since the disk dmg.
I can not record my voice as in the past with an external microphone; For some time while playing my recordings I hear my voice well but accompanied by a background noise a kind of sizzling very important while before the recorded recordings did not generate any noise or breath, it was really perfect and Of course always with the same microphone.
Below is a screenshot of the waveform that appears during recordings and is also displayed when the microphone is closed.

What is the machine and microphone? How are they connected?


My computer is a mac pro released in 2012 with mac os 10.12.6 and my version of audacityest 2.1.3.
I have the same problem on a mac pro 2007 model with audacity 2.1.1.
Thank you for your reply.

The microphone I use and a JB27 with the following features: Micro JB27 JB Systems
Professional Microphone
Very pure sound quality
Very good sensitivity
XLR Connector
Sold with Case, microphone clamp and 6m XLR cable / mono jack
Type: cardioid dynamic
Polarity: unidirectional
Frequency Response: 50 Hz - 18 kHz
It is connected to the computer at the input port of the mac pro.

That’s a dynamic mic on a line-level input?

The level is too low, so your mic connection picks up a lot of noise. You need a simple mic preamp.