kHz
I agree that a variable low-pass makes more sense when the A/D can work
at a multiple frequencies. My comments about the use of fixed filters
came from a couple of conversations with designers at AES this year; my
impression was that the practice is not uncommon.
Can you explain how an over-sampling A/D works into this equation? Does
it reduce the burden on the analog low-pass filter?
I've sent my Fostex contact a note to confirm the behavior (fixed vs.
variable) of the analog low-pass filter in the FR-2.
Rudy
On Jan 11, 2005, at 4:14 AM, wrote:
> Message: 8
> Date: Mon, 10 Jan 2005 10:53:59 -0800
> From: Dan Dugan <>
> Subject: Re: freq response and aliasing of Edirol FA-101 (and FR-2) at
> 192 kHz
>
> Rudy Trubitt, you wrote,
>
>> Most A/D designs have a fixed frequency analog input filter before the
>> A/D. If the A/D must operate at frequencies as high as 192, then this
>> fixed filter must be set high. The consequence of this (at least
>> theoretically) is that recordings made at lower sampling frequencies
>> (for example 44.1 on a device capable of 192) will have more aliasing
>> than would be the case if the input analog filter was set lower, to a
>> value appropriate for a 44.1 recorder, rather than a 192 model.
>
> If they do have a fixed low-pass filter, they're doing it very wrong.
> A multi-rate A/D should change the filter as it changes the sample
> rate.
>
> -Dan Dugan
>
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