Equalisation for PC mic input/line input

QUESTION:
Do the PC mic and line inputs use the same equalisation (on the
frequency spectrum)?


BACKGROUND:
I have some noisy voice tapes from an old analogue dictation machine.
I'm reading the recordings from the "ear" socket of my dictation
machine into my PC and then coverting the recordings to MP3.

Later I will get some software to clean up the noise on the MP3s.

I didn't expect it but my PC allows me to set a decent recording
level whether I record through the mic input or the line input.

Until I clean up the sound, the noise from the original recording
makes it hard to tell if I'm getting a better result from the mic
input or the line input.

I was wondering if there was a different equalisation used by the PC
for the mic and line inputs. If so then I would make sure I used


ANOTHER QUESTION:
What is the input level at which the mic and line inputs are rated?
I had thought mic inputs were about 3 or 3 mV and line inputs were
200 mV.

-------

NOTE:
My PC motherboard chipset is VIA KT266A + VT8235.
A PC reporting utility says it detects a VT8233/A AC97 Enhanced Audio
Controller.

"David Peters (UK)" wrote:
>
> QUESTION:
> Do the PC mic and line inputs use the same equalisation (on the
> frequency spectrum)?

There is not equalization with line input, i.e. it uses flat frequency response. I am not sure about microphone input; the biggest difference seems to be they operate at a lower signal level.

> BACKGROUND:
> I have some noisy voice tapes from an old analogue dictation machine.
> I'm reading the recordings from the "ear" socket of my dictation
> machine into my PC and then coverting the recordings to MP3.
>
> Later I will get some software to clean up the noise on the MP3s.
>
> I didn't expect it but my PC allows me to set a decent recording
> level whether I record through the mic input or the line input.
>
> Until I clean up the sound, the noise from the original recording
> makes it hard to tell if I'm getting a better result from the mic
> input or the line input.

You should use the line input with the headphone output, as both operate at relatively high signal level with flat frequency response.

> I was wondering if there was a different equalisation used by the PC
> for the mic and line inputs. If so then I would make sure I used
>
> ANOTHER QUESTION:
> What is the input level at which the mic and line inputs are rated?
> I had thought mic inputs were about 3 or 3 mV and line inputs were
> 200 mV.

Back in the days of analog recording 0 db was 1 volt. Since this was analog the 0 db level could be and was often exceed. With the advent of digital CDs the 0 db level became the maximum level, which can not be exceeded because of the digital format, and is supposed to be 2 volts. Since these are maximum levels the average will much lower.
Microphone levels are lower and vary widely.

> -------
>
> NOTE:
> My PC motherboard chipset is VIA KT266A + VT8235.
> A PC reporting utility says it detects a VT8233/A AC97 Enhanced Audio
> Controller.

--
Mike Walsh
West Palm Beach, Florida, U.S.A.

"Mike Walsh" <spamscks@netrox.net> wrote in message
news:44143D5F.C5A54A69@netrox.net...
>
>
> "David Peters (UK)" wrote:
>>
>> QUESTION:
>> Do the PC mic and line inputs use the same equalisation (on the
>> frequency spectrum)?
>
> There is not equalization with line input, i.e. it uses flat frequency
> response. I am not sure about microphone input; the biggest difference
> seems to be they operate at a lower signal level.

Microphone inputs are also flat, i.e. with no equalisation. As you say, they
operate at a much lower level, typically a few millivolts.

>
> You should use the line input with the headphone output, as both operate
> at relatively high signal level with flat frequency response.

Correct.
>
> Back in the days of analog recording 0 db was 1 volt. Since this was
> analog the 0 db level could be and was often exceed. With the advent of
> digital CDs the 0 db level became the maximum level, which can not be
> exceeded because of the digital format, and is supposed to be 2 volts.
> Since these are maximum levels the average will much lower.
> Microphone levels are lower and vary widely.

Not quite. Firstly, a dB is a relative level, not an absolute, so without
stating the reference, a figure of "xdB" is meaningless. Originally, 0dB was
referenced to a power of 1mW into a load of 600 ohms, and was referred to as
0dBm. Later, the same voltage level, but unloaded, that is, without
reference to a 600 ohm load became 0dBu (that is, unloaded) Note that the
voltage level is the same in both cases (0.775v, or 1mW into 600 ohm) There
was a strange semi-standard evolved of referring to 1V rather than 0.775v
and that was 0dBv.

Digital outputs are referred to maximum digital output (when all the bits
are 1) and that is called 0dBFS (0dB Full Scale). It has NO analogue
equivalent, as analogue can keep getting bigger without limit, digital can't
get any bigger than when all the bits are 1. In Digital-Analogue conversion,
a number of different conversion levels have become more-or-less standard.
The EBU (European Broadcasting Union) have defined 0dBFS digital to mean
+18dBu analogue after conversion. The USA prefers that 0dBFS = +24dBu
because that provides 20dB headroom above 0VU. A few dissidents prefer
+25dBu as that's 1dB better than +24...........

CD players have evolved a standard output of 2v analogue for 0dBFS, but as
far as I'm aware, there is no official standard for this.

S.

In message <44144794$1_1@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
<serge.auckland@tiscali.co.uk> writes
>
(snip)

>The EBU (European Broadcasting Union) have defined 0dBFS digital to mean
>+18dBu analogue after conversion.
>
>
Interesting.
Can you let me have a reference to the technical paper for that.
Cheers,
--
Kevin Seal (at home)
FZS600 in Banana
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

"Kevin Seal" <me@privacy.net> wrote in message
news:Ytv0xiJ2bGFEFwCI@news.individual.net...
> In message <44144794$1_1@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
> <serge.auckland@tiscali.co.uk> writes
>>
> (snip)
>
>>The EBU (European Broadcasting Union) have defined 0dBFS digital to mean
>>+18dBu analogue after conversion.
>>
>>
> Interesting.
> Can you let me have a reference to the technical paper for that.
> Cheers,
> --
> Kevin Seal (at home)
> FZS600 in Banana
> {kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}
>

EBU R68-2000. I'm emailing you a copy directly.

S.

In message <44146c1b$1_4@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
<serge.auckland@tiscali.co.uk> writes
>
>"Kevin Seal" <me@privacy.net> wrote in message
>news:Ytv0xiJ2bGFEFwCI@news.individual.net...
>> In message <44144794$1_1@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
>> <serge.auckland@tiscali.co.uk> writes
>>>
>> (snip)
>>
>>>The EBU (European Broadcasting Union) have defined 0dBFS digital to mean
>>>+18dBu analogue after conversion.
>>>
>>>
>> Interesting.
>> Can you let me have a reference to the technical paper for that.
>> Cheers,
>>
>
>EBU R68-2000. I'm emailing you a copy directly.
>
Received, thanks.

With 0dBFS as =18dBU, that would mean OVU (+4dBU) would be -14dBFS. Most
people I know line-up their Pro Tools rigs for -18dBFS for 0VU hence
OdBFS is going to be +22dBU.
Isn't it a lovely world!
--
Kevin Seal (at home)
FZS600 in Banana
{kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}

"Kevin Seal" <me@privacy.net> wrote in message
news:sstpR+K+YHFEFw0n@news.individual.net...
> In message <44146c1b$1_4@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
> <serge.auckland@tiscali.co.uk> writes
>>
>>"Kevin Seal" <me@privacy.net> wrote in message
>>news:Ytv0xiJ2bGFEFwCI@news.individual.net...
>>> In message <44144794$1_1@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
>>> <serge.auckland@tiscali.co.uk> writes
>>>>
>>> (snip)
>>>
>>>>The EBU (European Broadcasting Union) have defined 0dBFS digital to mean
>>>>+18dBu analogue after conversion.
>>>>
>>>>
>>> Interesting.
>>> Can you let me have a reference to the technical paper for that.
>>> Cheers,
>>>
>>
>>EBU R68-2000. I'm emailing you a copy directly.
>>
> Received, thanks.
>
> With 0dBFS as =18dBU, that would mean OVU (+4dBU) would be -14dBFS. Most
> people I know line-up their Pro Tools rigs for -18dBFS for 0VU hence OdBFS
> is going to be +22dBU.
> Isn't it a lovely world!
> --
> Kevin Seal (at home)
> FZS600 in Banana
> {kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}
>
Standard are great, that's why we have so many of them!

S.

On Sun, 12 Mar 2006 13:41:15 GMT, "David Peters (UK)"
<no-email@mail.com> wrote:

>QUESTION:
>Do the PC mic and line inputs use the same equalisation (on the
>frequency spectrum)?
>
>
>BACKGROUND:
>I have some noisy voice tapes from an old analogue dictation machine.
>I'm reading the recordings from the "ear" socket of my dictation
>machine into my PC and then coverting the recordings to MP3.
>
>Later I will get some software to clean up the noise on the MP3s.
>
>I didn't expect it but my PC allows me to set a decent recording
>level whether I record through the mic input or the line input.
>
>Until I clean up the sound, the noise from the original recording
>makes it hard to tell if I'm getting a better result from the mic
>input or the line input.
>
>I was wondering if there was a different equalisation used by the PC
>for the mic and line inputs. If so then I would make sure I used
>
>
>ANOTHER QUESTION:
>What is the input level at which the mic and line inputs are rated?
>I had thought mic inputs were about 3 or 3 mV and line inputs were
>200 mV.
>
>-------
>
>NOTE:
>My PC motherboard chipset is VIA KT266A + VT8235.
>A PC reporting utility says it detects a VT8233/A AC97 Enhanced Audio
>Controller.


The short answer is that for best results you should:

- use a quality tape deck with line-out, not the earphone
jack of a dictation system

- use the line-in on a fair quality sound card, not
integrated motherboard audio with a really cheap codec.

"Serge Auckland" <serge.auckland@tiscali.co.uk> wrote in message
news:44147a8e_1@mk-nntp-2.news.uk.tiscali.com...
>
> "Kevin Seal" <me@privacy.net> wrote in message
> news:sstpR+K+YHFEFw0n@news.individual.net...
>> In message <44146c1b$1_4@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
>> <serge.auckland@tiscali.co.uk> writes
>>>
>>>"Kevin Seal" <me@privacy.net> wrote in message
>>>news:Ytv0xiJ2bGFEFwCI@news.individual.net...
>>>> In message <44144794$1_1@mk-nntp-2.news.uk.tiscali.com>, Serge Auckland
>>>> <serge.auckland@tiscali.co.uk> writes
>>>>>
>>>> (snip)
>>>>
>>>>>The EBU (European Broadcasting Union) have defined 0dBFS digital to
>>>>>mean
>>>>>+18dBu analogue after conversion.
>>>>>
>>>>>
>>>> Interesting.
>>>> Can you let me have a reference to the technical paper for that.
>>>> Cheers,
>>>>
>>>
>>>EBU R68-2000. I'm emailing you a copy directly.
>>>
>> Received, thanks.
>>
>> With 0dBFS as =18dBU, that would mean OVU (+4dBU) would be -14dBFS. Most
>> people I know line-up their Pro Tools rigs for -18dBFS for 0VU hence
>> OdBFS is going to be +22dBU.
>> Isn't it a lovely world!
>> --
>> Kevin Seal (at home)
>> FZS600 in Banana
>> {kevin at the hyphen seal hyphen house dot freeserve dot co dot uk}
>>
> Standard are great, that's why we have so many of them!

Decibels, to me, seem to be overused, particularly with digital audio. And
particularly because silence is negative infinity decibels, which isn't a
lot of good if you're writing a computer program that can only cope with
real numbers. What's wrong with plain old 0% to 100%?!
(Rhetorical question, don't feel obliged to answer...)

On 12 Mar 2006, Serge Auckland wrote:

>>
>> Back in the days of analog recording 0 db was 1 volt. Since
>> this was analog the 0 db level could be and was often exceed.
>> With the advent of digital CDs the 0 db level became the
>> maximum level, which can not be exceeded because of the digital
>> format, and is supposed to be 2 volts. Since these are maximum
>> levels the average will much lower. Microphone levels are lower
>> and vary widely.
>
> Not quite. Firstly, a dB is a relative level, not an absolute,
> so without stating the reference, a figure of "xdB" is
> meaningless. Originally, 0dB was referenced to a power of 1mW
> into a load of 600 ohms, and was referred to as 0dBm. Later, the
> same voltage level, but unloaded, that is, without reference to
> a 600 ohm load became 0dBu (that is, unloaded) Note that the
> voltage level is the same in both cases (0.775v, or 1mW into 600
> ohm) There was a strange semi-standard evolved of referring to
> 1V rather than 0.775v and that was 0dBv.
>
> Digital outputs are referred to maximum digital output (when all
> the bits are 1) and that is called 0dBFS (0dB Full Scale). It
> has NO analogue equivalent, as analogue can keep getting bigger
> without limit, digital can't get any bigger than when all the
> bits are 1. In Digital-Analogue conversion, a number of
> different conversion levels have become more-or-less standard.
> The EBU (European Broadcasting Union) have defined 0dBFS digital
> to mean +18dBu analogue after conversion. The USA prefers that
> 0dBFS = +24dBu because that provides 20dB headroom above 0VU. A
> few dissidents prefer +25dBu as that's 1dB better than
> +24...........
>
> CD players have evolved a standard output of 2v analogue for
> 0dBFS, but as far as I'm aware, there is no official standard
> for this.


I can't say I understand all of what you write but the parts I do
understand are very useful to me. Thank you for posting.

Are there any web sites or documents which explain this sort of thing
for a beginner: rigorously but not going too fast.