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View Full Version : SB Sound quality (Danny Rego)



Rob MacLachlan
2004-09-30, 07:54
If you have any concern about sound quality of the Squeezebox v.s. CD
player, and are playing any kind of compressed (MP3) output, then you
should investigate your encoder way way before you start worrying about
external DACs and audophile digital cables. There are real
non-at-all-controversial reasons to believe that compression affects the
sound. MP3 is lossy compression based on a model of human hearing
limitations. MP3 by design does not give the same signal back.
As an experiment, try playing back a raw uncompressed .WAV file and see
if it is better. If this does not help, then compression is not a
problem.

I am told that 128 kbits/sec constant bit-rate MP3 encoding is audibly
different from CD quality. I have been using lame with -v -b 112, which
is a variable bit rate averaging about 160 kbits/sec, which supposedly
is near-CD quality. I can't hear the difference, but what the heck.

Try doing an A/B test with the CD player by changing the source on the
amp between the CD played and the SB. You must match the playback level
of the squeezebox so that it plays with the same loudness as the CD
player. A louder source will always sound better. This can't really be
done properly without using a meter and a test CD, but if the badness of
the SB seems not to depend on the SB volume setting, even when the SB is
clearly louder, then you probably are hearing a real difference.

It is conceivable that you have a hardware defect in your squeezebox,
but this would be unlikely to cause any subtle effect.

So far as the effects of different digital cables or even external DACs,
the effects are clearly only heard by a minority of people, and many
people with relevant expertise in electrical engineering and human
hearing performance tend to be skeptical that these effects exist at
all. See:
http://2eyespy.tripod.com/myaudioandhometheaterhomepage/id3.html

Rob

Robin Bowes
2004-09-30, 09:47
On Thu, September 30, 2004 16:44, Phillip Kerman said:
> Without getting on your case Rob, I do have to disagree with a few
> points....

Can we end the high-end audio flamewar here before it begins? :)

That said...

>> If you have any concern about sound quality of the Squeezebox v.s. CD
>> player, and are playing any kind of compressed (MP3) output, then you
>> should investigate your encoder way way before you start worrying about
>> external DACs and audophile digital cables. There are real
>> non-at-all-controversial reasons to believe that compression affects the
>> sound.
>
> This is definitely a fact. I think it's actually safe to say
> that--depending on the nature of the sound on the original CD--an MP3 will
> always sound worse.

Remember, this is subjective. Your ear becomes trained depending on the
amount of exposure you've had to audio sources of differing qualities.

>> I am told that 128 kbits/sec constant bit-rate MP3 encoding
>> is audibly different from CD quality. I have been using lame with -v -b
>> 112, which
>> is a variable bit rate averaging about 160 kbits/sec, which supposedly is
>> near-CD quality. I can't hear the difference, but what the heck.
>
> Yes, it has been stated that 128 kbps is near CD quality--who ever came
> up with that doesn't have very good ears however. I can definitely hear
> the difference between raw WAV and 320kbps MP3 in every piece of music
> I've ever tested. Sometimes it's very very subtle though.

This is a classic example of subjectivity.

>> A louder source will always sound better. This
>> can't really be done properly without using a meter and a test CD, but if
>> the badness of the SB seems not to depend on the SB volume setting, even
>> when the SB is clearly louder, then you probably are hearing a real
>> difference.
>>
>
> Not sure what you mean... the A/B should both be louder or the one which
> happens to be louder will sound better?

I think he means that, given two otherwise identical sources, the louder
one will sound better. In other words, when performing AB tests it is
important to ensure the levels are the same.

> I think---in addition to setting
> up a fair comparison for volume--one should also pick out a good piece of
> music. Generally, recordings of real live things: voice and accoustic
> instruments are easier to recognize as accurate or distorted because our
> brains know what they should sound like. Also a piece with a large
> dynamic range is good to test. MP3s really get crappy when you listen to
> changes from quiet to loud.

The important point here is to do one's own tests with the type of
music/audio one regularly listens to. Yes, it may be that classical music
(for example) with a large dynamic range does not sound too good when
encoded as mp3, but if you're a speed metal freak then who cares!

>> So far as the effects of different digital cables or even
>> external DACs, the effects are clearly only heard by a minority of
>> people, and many people with relevant expertise in electrical
>> engineering and human hearing performance tend to be skeptical that
>> these effects exist at all.
>
> I don't know. I just used an okay Dennon receiver's DAC and my Rotel's
> DAC and in both cases the sound quality difference was striking (compared
> to the internal DAC in the SB). Night and day almost.

More subjectivity...

> Regarding the cables. The digital coax cable I had at first (~$25) is
> notably worse at reproducing trebble... compared to the one with silver in
> it (~$50). The difference was very subtle though. And, I didn't bother
> looking at cables costing way more. The thought that these are low end
> cables is almost funny.

Yet more subjectivity!

> Anyway, I'd say a separate DAC vs. the one in SB is not a subtle
> difference.

I'd tend to agree with you, but it's still subjective.

> Regarding this link:
> http://2eyespy.tripod.com/myaudioandhometheaterhomepage/id3.html
>
>
> Looks like some fun reading. I can say with utmost certainty that some of
> the statements on that page are absolutely false. (Which, by the way,
> does not necessarily mean the rest are false.) For example, suggesting
> speakers don't experience a break-in period is misguided.

There are undoubtedly certain tweaks that can make a difference to how
your audio sounds but this entire area of the industry has been tarred
with the snake oil brush.

I think this is also a good exmaple of the law of diminishing returns.
Maybe $10,000 of speaker cable will make a difference to your $25,000
Krell amplifiers but will the whole $60,000 system sound $58,000 better
than a reasonable competent $2,000 mass-market setup? You've got to be
able to afford to have ears that can hear that sort of difference!

R.
--
http://robinbowes.com