Log in

View Full Version : I told my friend someone here would know... don't let me down! ;-)


bob[_5_]
September 22nd 09, 12:14 AM
here's his email. if anyone understands, woohoo! but if not, no
worries!!

So I am trying to determine whether or not the AI-3 adat converters I
have are 24 bit or 20 bit. I have two of these so I asked Alesis and
they said that all 24 bit units would have 24 bit screened above the
IEC power........ however........ I have one which came with the box.
On the box it says 24 bit, inside the box is a "late breaking" note
which says the unit is 24 bit despite what the prinitng on the unit
says, and on the back of the unit is screened 20 bit by the IEC
(serial number matches what is printed on the outside of the box). My
other unit does not say either way. I have looked at files recorded
with the unmarked unit and they claim to be 24 bit. To add further
confusion when I inquired at Black Lion they told me

"Both the 20 bit and the 24 bit units that have come in here use the
exact same converter chips. The differences between the two with
regard to bit rate would lie solely in how the two bit depth pins on
each converter chips are configured. If the pins are configured one
way the output of the converter would be 20 bit, if they are
configured a different way the output would be 24 bit. This would be
fairly easy to alter just by changing which of the two pins are tied
to voltage and which are tied to ground. Given Alesis' track record on
the issue, I'd bet that many of the 20 bit units are actually 24 bit."

When I asked them if they could do this modification they said no I
should find a local tech...... however........ how would I know to
begin with if the unit is ACTUALLY 24 bit or 20 bit and how are the
techs going know what to mod? Arghh. I get the feeling that the
current Alesis folk know not what they speak of but I'd love to be
able to see if you could determine this information by the serial or
through a recording test. Anyone out there an expert on these?

Scott Dorsey
September 22nd 09, 12:48 AM
bob > wrote:
>When I asked them if they could do this modification they said no I
>should find a local tech...... however........ how would I know to
>begin with if the unit is ACTUALLY 24 bit or 20 bit and how are the
>techs going know what to mod? Arghh. I get the feeling that the
>current Alesis folk know not what they speak of but I'd love to be
>able to see if you could determine this information by the serial or
>through a recording test. Anyone out there an expert on these?

My suspicion is that no matter how it's configured, it probably is
not giving more than 17 or 18 actually useful bits.

Run a bitscope application on your computer. Put audio in. If you
see 20 bits changing on the scope, you have a 20 bit converter. If
you see 24 bits changing, you have a 24 bit converter.

Then stop putting audio in. Look at the bitscope and see how many
bits are changing with no input. That gives you some notion of where
the noise floor is, and how many of the bits coming out of the converter
are actually useful.

If the unit is a 20-bit model, you can modify it so that it produces
more bits on output, but if those bits are not valid and meaningful,
it's not worth the trouble.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Mike Rivers
September 22nd 09, 01:10 AM
bob wrote:

> So I am trying to determine whether or not the AI-3 adat converters I
> have are 24 bit or 20 bit.

Before you worry your little head off, you should understand what 20-bit
and 24-bit means when it comes to A/D converters. It has nothing to do with
the number of actual accurate bits digitized (that's probably 17 or 18) but
only the number of bits in the output word. Given that the hardware is
the same for both "versions" there is no reason why a 24-bit version would
sound any different form a 20-bit version.

If you set your DAW to record 24-bit resolution, with the 24-bit one,
the last
four bits will be noise far below the analog noise floor. With the
20-bit one,
the last four bits will be filled out with zeros. The actual audio data
will be
the same.

So shut up and record something.

bob[_5_]
September 22nd 09, 02:09 AM
On Mon, 21 Sep 2009 20:10:46 -0400, Mike Rivers >
wrote:

>bob wrote:
>
>> So I am trying to determine whether or not the AI-3 adat converters I
>> have are 24 bit or 20 bit.
>
>Before you worry your little head off, you should understand what 20-bit
>and 24-bit means when it comes to A/D converters. It has nothing to do with
>the number of actual accurate bits digitized (that's probably 17 or 18) but
>only the number of bits in the output word. Given that the hardware is
>the same for both "versions" there is no reason why a 24-bit version would
>sound any different form a 20-bit version.
>
>If you set your DAW to record 24-bit resolution, with the 24-bit one,
>the last
>four bits will be noise far below the analog noise floor. With the
>20-bit one,
>the last four bits will be filled out with zeros. The actual audio data
>will be
>the same.
>
>So shut up and record something.

heh, i expected nothing less... thanks for both replies!