|Advanced Audio Recording|
Digital Upsampling of audio signals
In this example a digital audio stream is upsampled by ratio 3 in order to transform a recording from 32kHz consumer DAT to 96kHz in order to prepare it for post processiong. This article shows some technical background, why this is usefull: Do we need 96kHz ?
Insertion of Zeros
From the theory it is sufficient to insert zero values for non defined samples when creating the higher data rate and apply a filter. Pratically this has some issues:
Depending on the subsequent reconstruction filter, a non ideal reconstruction is achieved especially with BIAS loaded data streams. This is because of the non ideal filter curve which never meet the requirement of a perfect cut off frequency.
In this example a linear approximation in between the given data points is used to defined the missing values.
Here a dynamic interpolation filter is used to reconstruct the non existent values. It is a modified newton filter. In this case the data stream has less requirements regarding the reconstruction filter.
Conclusion and Summary
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