[swatson]

I have some children's songs that I played on a cassette player. Using the line out on the cassette player and the line in (mic) on my eMac I recorded the music with Audio Hijack.

The audio volume is very low compared to the rest of the music library, and the songs have the cassette "hissing" sound, especially when the volume is turned up to listen in the car or the living room.

What is the best way for me to remove the hissing sound? Are there special filters? A specific app I should use? Recommendations? Garageband? Shareware? Pro Software?

[zigzag]

It's just a guess, but does your cassette player have any Dolby noise reduction features? Was Dolby used in the original recording? It's possible that when you transferred the content to your eMac, the Dolby settings on the cassette player didn't correspond to the settings that were used for the original recording.

For cassette noise reduction to work, the output setting has to match the setting that was used on the original recording. In other words, if you record with Dolby B, you need to use Dolby B for playback, or you'll get strange effects like the one you're describing. It's a bit like encrypting a file - you have to use the same code to properly decrypt it. Similarly, if Dolby wasn't applied to the original recording, but you applied it on playback, you'll get weird effects.

If there was no Dolby applied to the original recording, you might be able to reduce the hiss with a filter, although I've never tried it with a cassette. Toast and similar recording software might have such filters. Some of the audio engineers around here should know.

Hope this helps.

[pfflam]

Try going through a headphone jack so that you can adjust the volume out . . . you want to adjust for the signal-to-noise ratio of the older analogue equipment . . .

. . . you also may be working with the 'equal loudness principle' (look it up) if you record the signal at a low volume . . . that will mean that the ratio of frequencies to one another will change ever so slightly when you boost the volume to compensate, making some unheard sounds seem louder . . so you will want to make sure to boost the signal out.

. . also Dolby seems like food advice.