Sunday, September 05, 2010
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Softwares Audio Mastering

Audio Mastering

If you are trying to run a web radio station then there are a few things you need to ensure. One of these is that you are broadcasting the best quality sound that you can. To acheive this you must ‘master’ the audio content before it is encoded. This mastering ensures your stream uses all the dynamic range it can. If you have ever wondered why your station doesn’t sound very loud or punchy against pro stations then this is why.

Mastering can envolve some very complex audio processing however the main parts are much simpler and here we tell you how you can do it for free!

If you are broadcasting using winamp using the SHOUtcast dsp then you are definately in luck. While there are a few multiband or mastering plugins avaiable in our experience there is one above all others. It is called ‘Stereo Tool’ and features multi band compression, 10 band eq, stereo enhancer, dual band limiter and a maximiser to really squeeze that last bit out of the stream volume (dymanic range). Even better the features that you have to pay for are not needed for web radio so you get this excellent quality tool for free!

One thing to note is that this is a DSP and winamp only lets you run one DSP at a time. The SHOUTcast encoder is a DSP so you need a way around this. Thanks to the guys at Spacial who have developed a DSP stacker allowing you to run both at the same time.

If you are already running the SHOUTcast DSP then get the DSP Stacker install it then get the Stereo Tool intall that as well then in winamp select the DSP Stacker as the DSP you want to use instead of the SHOUTcast DSP. Now get in the stacker add the SHOUTcast DSP and the Stereo Tool in that order. You can now use both together. You will find on the Stereo Tool that it has some default settings. One of these is called ‘web radio’ try this to begin with and you can then start experimenting.

 

Info

Stereo Tool is a Winamp plugin that delivers professional quality audio processing - for free¹.

Have you ever wondered why on the radio all songs have the same volume, while if you play CDs or MP3s, the volume and the type of sound changes all the time? That's because the big commercial radio stations use expensive equipment that ensures that all songs sound the same, and that they sound good on a wide range of cheap up to expensive audio systems. Now Stereo Tool offers you similar processing, which you can use while listening to your own music.

Many people have reported that the processed audio sounds better on their equipment than the original unprocessed audio.

Besides this, Stereo Tool offers a stereo widener which makes music sound 'fuller' and more 'spacial' (less is also possible), and it can repair phase shift problems in recordings (cheap CDs, vinyl, tapes).

¹ Although most options of Stereo Tool are free, some options that enable FM radio stations to sound louder than their competitors, as well as some options that enable broadcasting in stereo and adding RDS texts to the broadcast without using extra hardware are limited in the free version of Stereo Tool.
Currently, Stereo Tool offers the following sound processing options:

  • 10-band multiband compressor / limiter / clipper
    If one song contains a lot of bass, and the next contains a lot of treble, this filter can make them sound equal. The volume is also kept at the same level. Many people have reported that music sounds better on their equipment when using the multiband compressor. The clippers reduce sudden bursts of loud sounds, without causing pumping or other artifacts.
  • Stereo channel separation widening / narrowing
    With this you can move the instruments to the center, or further away from each other. This can be used among others to let both speakers play all the sounds at the same level (so if you only hear one speaker, you don't miss any sounds), and still keep a part of the stereo effect.
  • Stereo phase shift widening / narrowing
    Phase shift widening makes the stereo stand out more, which can make music sound more powerful. The instruments do not change position though.
    Phase shift narrowing can be useful if you have a mono output channel: Sounds converted to mono using this filter sound just as full and powerful as the original stereo recording. This enables transforming any recording to mono without audiable artifacts, and achieving better quality encoding for low bitrate MP3 files.
  • Phasing error (AZIMUTH) correction filter.
    Old tape recordings and many cheap CDs often suffer from severe phasing errors. These phasing errors can make listening very unpleasant, and when the phasing error changes over time the sound can seem to "float" around you. It can also cause severe artifacts when converting the sound to mono or when playing it on a surround system. This filter automatically detects and repairs such errors.
  • Center bass speaker filter
    In some very rare circumstances, playing sounds using a single (center) bass speaker can result in less powerful and deformed bass sounds. This filter optimizes the bass for playback on a single bass speaker.
  • Hiss reduction filter
    Stereo Tool contains a powerful hiss reduction filter that has almost no effect on the rest of the sound. Especially useful when playing older songs or when a lot of volume compression is used.
  • 3-level overshoot protection
    If your goal is to make the sound loud, the 3-level overshoot protection filter can remove the remaining peaks after all the other processing has ended. By using 3 levels, any pumping artifacts that would normally be caused by such a filter are reduced as much as possible.
  • Loudness filter
    This filter can make sounds up to 5 dB louder, without causing higher amplitude peaks in the signal, with very little effect on the sound. Especially useful for radio stations that want to sound loud.
  • Lowpass filter
    Useful if you want to feed the Winamp output into an FM transmitter. This filter can completely remove any FM pilot tone interference. Also useful to hear how a recording would sound on an AM station etc.
  • FM transmitter support
    The following options can be used to prepare sounds for broadcasting on an FM transmitter.
    • FM pre-emphasis filter
      Prepares the sound to be sent through an FM transmitter, such that the pre-emphasis step in the transmitter does not cause clipping. The multiband compressor and overshoot filters take into account that the FM transmitter will pre-emphasize the sound.
      For FM transmitters that do not contain a pre-emphasis filter, Stereo Tool can also output the pre-emphasized sounds.
    • FM stereo encoder
      The software FM stereo encoder enables broadcasting in stereo using a simple mono FM transmitter.
    • FM RDS encoder
      The software RDS encoder enables broadcasting RDS texts without using a hardware RDS encoder.
    The last two steps don't work on every sound card (details).

    FM transmitter support have been tested with a very cheap (€ 15,= / $ 20,=) mono FM transmitter. When enabling Stereo Tool, the orignal mono, dull, soft and sometimes clipped sound becomes stereo and as clear and loud as that of the big commercial stations.
    More sophisticated FM transmitters may contain filters that disrupt the signal generated by Stereo Tool (details).
  • Channel delay filter
    Play back one channel with a small delay to create a fake stereo effect.
    •