David,

I have no information as to what equipment was used. However, it is my 
suspicion that small mono machines were used. I have digitised some 600+ 
tapes over the past few months. Only a small percentage exhibit this 
fault. I think what I need to do is to look at the transfers again and 
establish what factors are common to those recordings which have 
crackle. I suspect they are all mono recordings and using only the left 
channel would be a workable solution.

It's odd. I sit in a darkened room listening to these things day in and 
day out. After a while these little glitches start to really get to you. 
  Reading the messages on this board helps keep me sane. Keep up the 
good work guys.

Best Wishes
Mike

David Lennick wrote:
> Dumb question (for various reasons, I can't listen to the file at the 
> moment). Were these cassettes all recorded on small mono portable 
> machines? Tapes made on these almost always have a crackly or noisy 
> right channel when played back on good decks and in stereo. The solution 
> here is simply to play only the left channel.
> 
> dl
> 
> Mike Hirst wrote:
>> Thanks Richard,
>>
>> your advice is, as ever, well informed sagely and intelligent. I 
>> suspect that I'm not going to find a definitives answer here, but for 
>> your interest, and for anyone else who may be interested, I've posted 
>> a 10sec  (wav) clip of the kind of crackle I'm hearing. this sort of 
>> thing will continue through the full length of the recording and can 
>> be heard when the tape is played back using multiple recorders, all of 
>> which have been tested using other tapes, which exhibit no such problems.
>>
>> http://www.mikehirst.netfirms.com/audio/rhclick.wav
>>
>> filesize= 1392640 byte(s)
>> riffsize= 1764036 byte(s)
>> format  = Straight-PCM
>> channel = 2
>> depth   = 16 bit(s)
>> blk.size= 4 byte(s)
>> smp.rate= 44100 Hz
>> samples = 441000
>> playtime= 0:10.010
>>
>> you will note from the clip that the crackle can only be heard in the 
>> rh channel. this is typical of the phenomenon, but it can sometimes be 
>> heard in both channels (with a bias towards the rh ch).
>>
>> I have experimented with some of the de-crackle filters I use when 
>> working with disc transfers and as Richard suggests, the crackle can 
>> be removed, I am however curious as to where the crackle comes from.
>>
>> Richard L. Hess wrote:
>>> Hello, Mike,
>>>
>>> Tom Fine has already posted a number of good explanations.
>>>
>>> There are, however, less-common explanations that you may wish to be 
>>> aware of, just in case.
>>>
>>> (1) If there is a mismatch between the record machine record and 
>>> erase head track position, perturbations in the record bias and/or 
>>> erase MAY print to a tape like this. DC-(i.e. permanent magnet) erase 
>>> may also cause something like this, but it is usually more of a 
>>> "burbling" or what is sometimes called "rocks".
>>>
>>> (2) Static electricity and PLAYBACK machine "glitches" CAN print to a 
>>> tape without the recorder being in record mode. It's uncommon 
>>> (thankfully),  but it can happen. Static can be generated by fast 
>>> winding in a very dry environment, and depends on cassette materials 
>>> including the shell and slip sheets. This is more prevalent with 
>>> reels than cassettes.
>>>
>>> This clicks can usually be removed (depending on their source) by a 
>>> declick/decrackle plug-in for your favourite DAW. The Magix 
>>> restoration tools version of this is the best I've yet owned, but I 
>>> haven't owned either DC7 nor the high-end Algorithmix version.
>>>
>>> At 08:53 AM 2008-09-18, Mike Hirst
>>>> Here's a thing that's been confusing me for some time. I have spent 
>>>> the past six months working my way through a large number of 
>>>> cassette tapes mostly recorded between 1985 and 1995. every now and 
>>>> again I notice light, but significant crackling. This is often more 
>>>> noticeable in the right channel, but not exclusively so. On some 
>>>> recordings this is louder, on most recordings this is not evident at 
>>>> all. This is not restricted to any one brand of cassette, nor is it 
>>>> associated with any one playback machine and/or soundcard. Can 
>>>> anyone explain this for me?
>>>
>>> Richard L. Hess                   email: [log in to unmask]
>>> Aurora, Ontario, Canada       (905) 713 6733     1-877-TAPE-FIX
>>> Detailed contact information: 
>>> http://www.richardhess.com/tape/contact.htm
>>> Quality tape transfers -- even from hard-to-play tapes.
>>>
>>
> 
> 

-- 
Mike Hirst
Managing Director
DAS-360°
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Whitley Bay
Tyne & Wear
NE26 1AL

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