With the growth of music streaming services and how they deliver music to the consumer is changing the way we need to mix and master content, especially for music streaming services. In this article and free video tutorial in conjunction with Nugen Audio, our own loudness guru Mike Thornton demonstrates the importance of True Peak metering and limiting and how they can help prevent the consumer getting distorted tracks.
What Is Different When Mastering For Streaming Services
When we master for CD manufacture, the whole delivery process was lossless, usually 16bit 44.1k sample rate. Streaming inevitably means codecs - people are not listening to your WAV or AIFF, they are hearing an AAC or Ogg Vorbis version. These files don’t behave as nicely as the audio in your DAW, and what sounds great in the DAW may not sound the same when encoded for streaming. Almost no-one is listening to your mixdown in its original form, and with the overwhelming popularity of streaming services you simply cannot afford to ignore these downstream processes.
Codecs Don’t Like It Hot
Codecs struggle to handle hot audio, which can lead to distortion in the audio stream that was not present in the original master. The space between the samples is where trouble lies; in these gaps the analogue waveform continues smoothly, so in some cases the reconstructed waveform can be higher than the sample measurements either side. This is known as an 'inter-sample peak', and it results in distortion as the waveform is incorrectly reconstructed. The secret to avoiding codec distortion lies with inter-sample peak measurement and limiting.
You Need A True Peak Limiter
With this in mind, a True Peak limiter such as ISL from Nugen Audio is an essential part of the tool set. The harder you push a traditional sample peak limiter, the more likely you are to introduce inter-sample peaks, and you won’t necessarily hear the problem until you export your mix and encode for streaming.
It may seem very picky, but did you know that when you convert the digital audio back into analog, the reconstructed waveform between the samples, the intersample peaks, can be up to 6dB higher and as we are working very close to digital headroom and processing audio with codecs that are not very good at handling audio close to digital headroom we need both metering and limiters that work to something called true peak.
What is True Peak
True peak meters will display what is likely to happen between the samples when the audio is converted back into analog and so we can also be confident that we will not overload the lossy codecs and so end up with distorted tracks being delivered to the consumer. This is achieved using a technique called oversampling which enables us to measure the intersample peaks, what is going on between the peaks, and so make sure that we do not try and exceed digital headroom between the samples. We can then adjust our levels so that our carefully crafted tracks are not going to be distorted by the time the consumer listens to them.
Mastercheck from Nugen Audio has a true peak meter and it is recommended that if your mixes are going to be converted into mp3s that you make sure that your audio doesn’t go above -3dBTP and for AAC files you can go up to -1dBTP.
So Now We Can Measure True Peak, What About The Limiter?
As well as having a meter like MasterCheck that can display true peak it is also very important that your mastering limiter is also working to true peak. Most limiters, either hardware or software are not working to true peak, and you can safely say that if they don’t shout their True Peak credentials from the roof tops then they are not true peak, and although there is no reason why you shouldn't carry on using your favourite dynamics processors in the production process, when it comes to the final mastering phase having a reliable and accurate true peak limiter is essential.
In The Free Video Tutorial
In this free video tutorial, we demonstrate this with an instance of MasterCheck from Nugen Audio and feeding it from a limiter plug-in that isn’t a true peak limiter. Even though the threshold of the limiter is set to -6dBFS the true peak meter shows true peaks that are much higher.
Then we show that if we add an instance of ISL2 from Nugen Audio after the sample peak limiter with the ISL2 threshold set to -6dBTP there is some gain reduction. With a second instance of MasterCheck on the output of the ISL2 limiter and all is as you would expect. No peaks above -6dBTP.
That’s It For Now
I hope you have found this mini series of free video tutorial and articles helpful in understanding how the workflows and techniques have changed now more and more music is being delivered to consumers using streaming services that use loudness normalisation to keep their customers happy so they don’t have to keep turning the volume up and down.