I am converting hypnosis cassette tapes to mp3 - the tape cassette plays well and the recording is clear but once I have uploaded this to Audacity there is a harsh crackling sound when the speaker is talking? I have reduced input volume, done effect - noise reduction but not sure how to go any further - any help would be welcome. 
It sounds like the input volume is too loud. Choose View > Show Clipping. Do you get red lines where the speaker is? If so the voice is too loud.
Please read the pink panel at the top of the page and give us version of OS X and version of Audacity. What is the make and model number of the cassette player? What type of Mac? How are you connecting the tape player to the Mac?
Gale
In order of your questions.
No I do not get red lines and indeed have put input volume right down to 4 on the slider scale thinking this must be the problem - it did remove static but not the crackling which only happens when there is voice.
I am running OX 10.9.4 and audacity 2.0.5.
I am using a sony cassette-corder CFD-E100L and connecting it via a cable from headphone slot to the desktop mac input microphone slot.
Any suggestions would be welcome!
Presumably you have only this one audio input on the Mac? What is the exact model number of the Mac?
Can you attach five seconds of voice that has the crackling? Please see How to post an audio sample .
Gale
I am using Mac desk top circa 2009 2.66 GHz Inter Core 2 Duo, it has separate jacks for input and output - I could not get my laptop to work.
I am having trouble uploading WAV file as they are above 1M - have uploaded it to dropbox but unsure not to link it to this forum - apologies I learn on the job so to speak.
regards
If you just drag-select five seconds of distorted voice in the blue waves then do File > Export Selection⌠and export as WAV, the file will be less than 1 MB.
You would right-click over the file and choose the option to share it. Then give us the web address of the file from the address bar in your web browser.
Gale
https://dl-web.dropbox.com/get/Child%20Esteem%202%20-%20selection.wav?_subject_uid=244019762&w=AAAo9vzWrB0b13LCHu_hHgINQ0lAqOevMZ--bhhgAprLFg
let me know if this works
âResource could not be foundâ occurs when I click that link.
Gale
hopefully this will work!
Mavericks living up to its name again. It sounds and looks like small dropouts.
Is it a MacBook Pro?
Are you running lots of different applications while recording, or running Skype?
If thatâs not the case, Audacity > PreferencesâŚ, Recording section, and try a different âAudio to bufferâ setting.
Gale
Working on an old desk top - no apps running but put Audio to Buffer to 80 and it seems to have sorted the problem for the last tape I have done - lets hope it works for the rest.
Thank you for your help. 
What value was âAudio to Bufferâ at before?
Gale
100
Thanks, that was default value.
Reducing the buffer normally runs the risk of causing dropouts, but sometimes lower settings are required on Mavericks with Audacity.
Gale
First of all, you can not to connect the line level output signal from the cassette tape deck to the microphone input connector of your computer (desktop or laptop).
The microphone connector is made to handle a microphone level signal (-57 db). The cassette tape deck has line level signal (-10 db).
Some desktop computer audio cards have an analog audio line level signal connector (for example: Creative SoundBlaster series). You can use it directly.
Normally, laptop computers audio cards donât have one. So, you need an analog to digital USB interface which has a line level signal stereo connector (most of them have one).
Greetings!!!
This is all true, but this is the Mac board. 
Until the advent of the combo input/output, most Macs only had a line-level audio input and no mic input at all. The posterâs sample file was not excessively loud and presumably they have a line-level input although they called the input a microphone.
Gale