If you are self-employed...(1099s or cash) and using the Schedule C...Check out section 179 expense (form 4562). You can get the form and instructions on irs.gov in PDF format to print out.
It\'s a form of depreciation (which is what I\'d think you need to do with your sound libs), that allows you to expense the total cost (given certain limitations) in the current year. Any amounts not allowed under that year can be carried over to the following year. I think the limit is like 20k, but also limited by your income (ie..you can\'t expense off more than you made). (but, you can write it down to zero and carry over the remaining amount to the following year).
There are rules about which \"asset\" types can be decpreciated under sec 179. There are rules about using this decduction. You must keep a written record of date it was placed in service (or bought) and a full description of it along with it\'s total cost. And you must keep in that written record, how much you elected to expsense using 179, any remaining balance so forth. Just use a log book or note book you keep with your tax stuff. Usually, you\'ll write most stuff off within 2 years (or have it completely expensed out). But, the IRS requires you keep such a log for 179 expense items.
When you fill out 4562, use a generic description of the type of item it is you are expensing. You \"can\" group certain things bought in around same time. For instance...my monitor, computer, printer, etc..all purchased as part of \"one\" computer.
I list such things as \"electronic equiopment\" on the 4562 description. Leave the details for your Log...should have serial numbers etc in there too.
\"supplies\" are wearable items...and usually low cost things. You might consider your replacement cables supplies (unlesss you are talking about a PA snake that cost a lot of money) under supplies. Paper for your printer. Consumables. etc. Printer cartridges. Items generally under 100 dollars.
Hope that helps