Q. Do I need to use a compressor before my soundcard?

By Sam Inglis

If I limit using a Alesis Nanocompressor when recording into my Emu 1820 soundcard, can I still limit the final mix with, say, Waves' L1 Ultramaximizer without any problems? I thought that you should only limit once, and then you have to unlimit before limiting again. Is this true or will the Nanocompressor cause no problems? I've set a threshold of just under 0dBFS and a ratio of 100:1. The attack is fast, and the release 200ms. Soft-knee and peak-sensing modes are active.
I am using the compressor to drive the A-D converters on the Emu 1820. Will this cause me any problems when limiting later to record to CD-R? Or should I just compress slightly at 2:1 with a -9dB threshold and fast attack and release times when recording at the input stage?

Thomas J

Features Editor Sam Inglis replies: I'm afraid there is no such thing as 'unlimiting'. Once you have applied dynamic processing such as limiting or compression to a signal, there isn't an awful lot you can do to reverse it. However, it's not uncommon to apply multiple stages of compression. Compressing an entire mix is also very different to compressing an individual signal within the mix, both in terms of what you're trying to do and the settings you would use.

Some people like to use a hardware compressor before the A-D converter, if it has a specific 'sound' that they can't get later using plug-ins. However, in normal use, there is absolutely no need to use either a compressor or limiter to 'drive' the A-D converters.

You only need to use a limiter on the way into the soundcard if you are dealing with wildly unpredictable levels and there is a possibility of a rogue peak exceeding the headroom you've left. In general, it would be much better simply to leave more headroom at the input of the A-D converter. The dynamic range of a modern A-D converter is huge, and there is no need to push your input signals anywhere near clipping in order to get good sound quality.

So, in short, unless your input signal levels are hugely and widely variable, or you particularly like the sound of the Nanocompressor, I'd simply remove it from the signal chain altogether, and turn the preamp gain down.

Published June 2005