Warp vs Other Sound Processing Strategies

Jennifer GrothBy Jenny Groth

The old story about FFT etc compared to Warp somehow got all muddled in the telling. FFT, IIR and FIR are digital filters. We use all of these types filters in our compressor, in our feedback cancellation, in our directionality and all over the place and so do all the other manufacturers. The point that whoever made up this story in the first place was trying to make was about system architecture, not about demonizing digital filter types. And even that point is probably not even valid anymore since it was mostly in relation to our own old architecture from Canta.

Although we don’t ever seem to clearly define it, “Warp” refers to the whole compression system. So it’s the “Warp compressor”, or the “Warp-based compressor”. This compressor has lots of different characteristics, but the one it takes its name from is that it uses Frequency Warping to define the band structure of the digital filters (be they FIR, FFT or whatever). Frequency Warping is a technique to map the frequency analysis directly to a logarithmic scaling. By using appropriate warping parameters, we get a scaling that is very close to models of the critical bands of the human auditory system. This is an efficient technique and lets us use some of our processing power on other fun stuff (note that this doesn’t necessarily mean that we are faster or better or more efficient than the way other manufacturers have designed their systems). Apart from human auditory system frequency resolution, another audiological benefit of using frequency warping is a frequency dependent delay that replicates the temporal delay of the traveling wave on the basilar membrane of a healthy ear at moderate input levels. This could ameliorate the temporal smearing caused by amplification (although not the temporal smearing caused by the cochlear pathology itself).

Everything in our Warp compressor is designed to compensate for these impaired characteristics. We already were doing a good job of meeting the frequency resolution, fast-acting and compression ratio demands (compressing a 120 dB range into an approximately 60 dB range as the cochlea does), but the Warp technique eliminates technical issues associated with delay and adds the temporal aspect as an advantage.  

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3 Responses to Warp vs Other Sound Processing Strategies

  1. Dan Schwartz says:

    When you use the term “Frequency Warping” are you referring to shifting the center frequency of each bandpass filter; or to shifting the output frequency slightly to reduce instability (“feedback”)?

    • gnresound says:

      This could more correctly be called “Frequency Warping Transformation” in that it is referring to taking a uniform spectral resolution and transforming it to a new, non-uniform frequency scale. So it’s more like when you say shifting the center frequency of each bandpass filter. It is not shifting the output frequency to reduce feedback.

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