Whistle When Using Sound Card as Pass-Through

On Wed, 20 Aug 2008 14:53:45 -0700, Michelle Steiner
<michelle.RemoveThis@michelle.org> wrote:

>> Well, the circuitry for the on-board audio components probably only
>> cost pennies. But that's hardly the point. He's feeding a socket
>> marked "Line In" with a signal that wants to go into one marked
>> "Phono".
>
>That's not the point; the OP said he gets that whine even after
>disconnecting the turntable from the input.
>
>And you don't have to lecture me about phono in; I've known about RIAA
>equalization for more than thirty years.

Might be interesting to see if the noise goes away when running on
battery with the power supply disconnected. As we all know, laptops
(even Macs are notoriously prone to this problem, and it won't be
helped by the mismatched source.

"Soundhaspriority" <nowhere.TakeThisOut@nowhere.com> wrote in message
news:6IKdnbOmLOdqLTHVnZ2dnUVZ_tzinZ2d@giganews.com
> "Michelle Steiner" <michelle.TakeThisOut@michelle.org> wrote in
> message
> news:michelle-2B67C0.14515220082008@news.west.cox.net...
>> In article <6h3douFi2sf8U1.TakeThisOut@mid.individual.net>,
>> "Richard Crowley" <rcrowley.TakeThisOut@xp7rt.net> wrote:
>>
>>>>> He gets the whine because he has a cheap built-in
>>>>> sound interface with the gain turned WAY up. Life is
>>>>> like that.
>>>>
>>>> Why do you say that the sound interface of the MacBook
>>>> is a cheap interface?
>>>
>>> ALL built-in sound interfaces are CHEAP. By definition.
>>
>> You're making an assumption; that's all.

> It is a correct assumption.

Agreed.

> Scott, Lawrence, and Richard
> said as much. To elaborate, everything sits on one board,
> with DC-DC converters in close proximity.

Which is not appreciably different from just about any other modern
mixed-signal application.

> Part of the
> construction of a good preamp is enough separation and
> enough metal to keep things separate.

This argument has some relevancy if you're talking true pro-grade mic
preamps, but PC audio interfaces are essentially line-level devices. Raising
the signal level by 40-60 dB makes a difference.

It is a basic fact of life that the basic nature of every ADC and DAC chip
puts logic-level digital signals in very close proximity to line-level audio
signals. There is no amount of money that can alleviate this basic fact of
life.

> This is simply not possible in a laptop.

False distinction - it is not possible to separate these signals any further
in a high end stand-alone DAC or ADC. I daresay that there are products out
there with the latest-greatest high end audio chips in them that are as
cramped as a laptop.

There is this insane idea that high end audio converters lack digital
signals in close proximity to audio signals. They've got Part 15 stickers on
them just like a PC, and they might even have switchmode power supplies. But
the basic digital input-output and clocks are there, regardless.

They perform very well, thank you.

> Space is at a premium. Since the noise floor is limited by the cramped
> space, there's no
> incentive to put in good parts.

Completely wrong. The problem is not the space, the problem is the budget
for buying parts. I have had no success in finding the actual sales price
of say an ALC 888 audio chip in *any* quantity, but I suspect it is less
than $1.00. That all said, the ALC 888 performs only a little worse than
Manna from Haven by 1978 standards.