On Wed, Nov 26, 2014 at 12:06 PM, Lokkerman <phil.steeples@gmail.com> wrote:
Some sound DBX'd – do you know of a plug-in for DBX? as I have ultimately toyed with recording them flat to analogue R2R and them playing them back with a DBX decoder to see how they should sound?
DBX (Type 1) applies (a lot of) HF preemphasis first, then 2:1 full-band compression. It is extremely sensitive to level and frequency response anomalies, and exact calibration or medium is a must. To make matters worse, DBX is not a multi-band compander, but compands the whole spectrum uniformly (Even Dolby A used 4 bands for this) so replicating algorithms used on compression more or less exactly is mandatory. Which would in digital domain require a FIR filter.
Therefore, trying to "de-DBX" a digital recording of a signal, is very tricky. To start with, RMS measurement should be 32bit, and very fast (floating point, etc)
If indeed this recordings are DBXed. You should hear extreme high frequency content, combined with 1:2 (extreme) compression, constant and sharp volume changes, all sounding very harsh, practically unplayable. Is that what you are hearing?
Try applying -0.5 (de)compression, with 1200ms release and 50ms attack, 40db floor, then do some low-pass sloping from 800Hz upwards, ending with -15db at 15kHz. If the result sounds dramatically better (but still "pumping" and harsh) you may have a DBXed recording :)
In which case, if the recording is valuable, I suggest a visit to eBay, and finding an used DBX Type 1 unit (100-200$)
Andrej
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