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The Brave New World of DSPs

Blog Post created by tvbsubbu Employee on Mar 15, 2018

Imagine traveling in a time machine across 140 years, listening from passive gramophones to the latest 16-channel audio video receiver (AVR), and the results would be amazing. It could be bit isolating, too. In the 19th century when the gramophone was playing, the neighbors and folks in the village and towns all gathered to listen and enjoy the sounds together. When it came to listening to a 16-channel AVR, I was the only one in my living room. Transformation in the society aside, there was a major change in dynamic range and fidelity, increased channel count and of course decrease in noise levels. Processing power with higher resolution and accuracy is one of the major elements for this transformation.

 

Analog Devices integrated Digital Signal Processors in the mid 80’s and these were 16-bit fixed point processors. The Harvard Architecture used in these processors made them very efficient. The first audio products using these types of processors were players with 2-channel decoding and post processing. The 2-channel decoders running on these processors did use double precision mathematics and output 24-bit audio. As a software hobbyist, and probably because I was a novice in signal processing, I used to spend significant time tuning these fixed-point processors and getting the desired characteristics from the filters. The major problem was decimation and truncation errors, and the laborious trial and error tuning of filter coefficients was the only solution. Subsequently, some of the simulation software packages did generate coefficients for fixed point processors, but didn’t eliminate the hand tweaking process completely.

 

Floating point digital signal processors were a boon and brought multiple advantages including better dynamic range, higher resolution, and lower noise. Soon enough the professional audio industry realized these benefits and used them in high end studio equipment with multiple processors on each board. Then equipment in movie theaters had audio decoders running on these DSPs. As one might expect they also migrated to AV Receivers for decoding and post processing bringing the experience of a theater in to their living rooms.

 

Good tool chains for these processors helped writing code in C/C++ and also use some of the highly optimized libraries for FIR, IIR, FFT/IFFT, etc. Programing in C reduced the time to market and brought portability across processors without deep knowledge on the processor architecture and latent. Example, IP holders may release multiple versions of a decoder correcting bugs or for bringing improvements and provide a new code in C/C++ with a few changes. Efficient processor compilers can create the new libraries for the processors with lesser effort and time as compared to doing this task in assembly.

 

That was just a helicopter’s view of the advantages that came with time. In my next blog, I will attempt a deep dive into processor architectures and how this has helped the audio industry.

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