Earlier this month we ran a poll asking you Which True Peak Limiter Do You Use? and three factors became clear. Firstly there is still confusion about which plug-ins are, and are not true peak limiters, exactly what is meant by true peak, and that there were a number of true peak limiters we didn't include in the first poll.
What Is A True Peak Limiter?
Most limiters base their limiting on the sample data in the digital audio signal. This type of limiter can only respond to the sample values and cannot respond to what might happen between the samples.
Whereas true peak limiters do respond to what might happen between the samples, using oversampling technology to predict what happens between the peaks and also to show what will happen when the digital audio is converted back into analogue, which will happen at some point as our hearing is still an analogue system. A simple rule of thumb is that if the limiter doesn't make a song and dance about being a true peak limiter or having oversampling as a feature, then it won't be.
Why Do We need True Peak?
All digital audio must be converted back to analogue at some point so we can hear it with our analogue ears. As part of this D-A conversion, a reconstruction filter is applied to round off the stepped digital audio signal. This is an issue when working close to digital headroom and especially when audio is processed through 'lossy' codecs like mp3, AAC or mp4.
Whatever type of work we are undertaking, broadcast, post or music, the closer we work to digital headroom the more important it is we know what is happening between the samples and what will happen when digital audio is converted back into analogue. We need tools that know where the true peaks are.
What Is True Peak?
When we convert analogue audio into digital audio the analogue to digital converter take a series of samples or snapshots of the analogue signal. As long as you take enough samples per second then it is possible to reconstruct an analogue waveform that very closly resembles the original analogue signal. When it comes round to converting the digital audio back into analogue, there is no data describing what happened between the samples. Just as in video or film, we only capture individual frames, anything that happened between the frames is not captured.
Coming back to digital audio we don't have any data between the samples. Look at the graphic below, we have two graphics representing the sampling process.
- The black wavy line represents a segment of an analogue waveform, the green vertical lines represent the sampling points when capturing digital audio.
- The blue lines represent the additional sample points when you oversample, giving data for what happens between the samples.
- The red lines show where the audio went over digital headroom between the samples.
Which True Peak Limiter Do You Use? - Results
Which True Peak Limiter Do You Use? - Results From 1st Poll
As you can see, the results above show that the 'Other' category was the most popular with 36% of the votes making the poll inconclusive because of the number of limiters not included.
Which True Peak Limiter Do You Use In Pro Tools? - New Poll
Thanks to all the community members for bringing all these other analogue peak limiters to our attention, so we are going to run a new poll which will include all the true peak limiter AAX plug-ins recommended by yourselves as well as some more that we didn't include in the first poll.