ChicoOG

After spending a boatload on after market audio gear (see sig below) I am really noticing the difference in sound quality produced by each source. CD's seem to be the most consistent, and I can always count on superb sound from XM71 Watercolors, my iPod on the other hand is sketchy. I notice various artists consistently sound good: John Mayer, Van Halen, Santana, Etc...others are a mixed bag...Robin Trower, Aerosmith, Eminem...I've played with some of the iTune filters and it seems to be better. Wondering if anyone else has noticed the same inconsistencies and what remedies are recommended.

Thanks for any input.

Knertified

CDs will always be the best... its an uncompressed waveform i think around 44khz/320kbits. I think DVDA's can go up to 96khz, not sure on kbits.

XM will differ per channel. Some of their channels stream at higher rates than others. My guess is the better sounding channels run at 128k compressed (near cd quality) and 96k compressed (lower than cd quality).

IPOD should sound as good as XM assuming the MP3's you have are atleast 128kbps and they are ripped correctly from the CD. Some people dont rip MP3's digitally which loses alot of quality.

So to answer your question, CD/DVDAs will always have the upperhand when comparing to compressed audio such as XM or MP3.

Knertified

Just noticed your Zapco amps. Very nice setup indeed. I recently came from a JL setup with Focal Utopias so I know what your talking about. Mastering is really the problem I think. I believe record companies master music for an "average stereo system". This causes all sorts of problems on high end systems because usually the EQs change dramatically on each track. Rap is a perfect example with it always having loud highs and loud bass. Its very frustrating at times. Electronic music is the same way. I wonder if there is an active sound processor out there that can normalize sound.. hmm..

ChicoOG

I've heard good things about Focal, are you running Zapco amps?

I believe mastering IS the culprit. It's amazing how different each artist sounds and what tones are highlighted in each genre.

Regarding the iPod, I've just been downloading stuff from iTunes. I've started playing around with their "EQ" with varying success. Does downloading stuff straight from CD improve the sound quality produced from the iPod?

Thanks for the input

Adobeman

CD - Most consistant. Best potential. Only "bested" by DVD-A (not like my GUI ones, the real 96k/24 bit ones from the store)

XM - All over the map for quality. Some channels are quite "unlistenable/dog crap" and at best it sounds like a well made mp3. Watercolors does seem to be at the top of the sound quality scale for XM. But for the price I get it and the number of channels I guess it's OK.

iPod - All over the map for quality. Depends entirely on how well the material was encoded to the format you are using and how connected to the car. Wav and Apple Lossless are your best bet but biggest files. I settled on LAME (I do not like iTunes mp3 encoder) using a VBR preset called "extreme". It strikes a good balance between portability, size and sound quality but is not anywhere near the quality of the CD it was made from. Sounds good in the headphones but whan played through a good system you can hear the difference for sure. I think the compromise is worth it given the amound of music and everywhere I can take it. Direct connection is the only way to go if you ever want to "salvage" any possibility of good sound from the iPod.

Lastly Focal drivers are know for being very high quality. Other names like Seas and Vifa are decent if you want a lower price point. I generally use Seas and Vifa for home speakers I build but don't do to much in the car with them.

ChicoOG

I've heard good things about Focal, MB Quarts, Treo, and others. I went with Zapco speakers, designed a manufactured by their sister company ESB in Europe who apparently does high end home audio stuff as well. There are very nice sounding compenents...

I found the LAME product you mentioned...looks very promising. I'll play around with it for a few days to see how it works. Thanks again.

Knertified

I was running a JL300a4 amp at the time. I had the Utopias in the front and a set of MB Quart ref premiums in the rear. The Focals were components and the MBquarts were coaxials with mounted tweeters. Unfortunately, my old car didnt have adiquete door space for the utopias which caused lots of sound issue. Now that I have the TL, I'm going to reattempt everything. I decided to go with some Focal polyglass speakers for the rear. I already had an idmax sub and 1000wrms amp. I noticed someone was able to install an 8inch w3 into the stock location ahd seal up the opening. I'm considering that now too. Anyways I should have some of it done this weekend. Ill let you know how it goes.

Desert_TL

CD: If you want to think of a CD in terms of bitrate, a regular CD holds 700MB or 80 minutes of music. A quick series of calculations results in a bitrate of 1.167 megabits/sec. CDs are typically sampled at 44.1khz. Any additional sampling (such as DVD-A's 96khz) will not result in any additional human-perceivable audio quality. The highest frequency humans can hear is about 20khz, and according to nyquist sampling theory, 40khz sampling will result in reproduction of the entire human hearing range. Any additional sampling is unnecessary. (Insert discussion of discrete Fourier transforms here. Unless you have a degree in math, physics, or electrical engineering, then a discussion of DFTs would be beyond your comprehension, but go ahead and look it up in Wikipedia if you feel so inclined.)

iPod: I assume you have loaded your iPod with MP3s you downloaded from the internet. MP3s can have a WIDE range of bitrates. The bitrate of the MP3 is the number one indicator of its quality, but not that only one. Some MP3 encoders really suck and will produce crap even if the bitrate is high. The "typical" bitrate when MP3s were first produced is 128kbit. This is the minimum required for even remotely nice sounding audio. I have seen 96kbit all over the internet. 192kbit is maybe 1/3 or 1/2 CD quality. If you listen to a 128kbit MP3 (the most common bitrate) and then listen to a CD recording of the same song, you will be SHOCKED at how much better the CD sounds. You get used to listening to MP3 and you think that's what the song should sound like, but you would be mistaken. Even 192kbit, the highest common bitrate found online, pales in comparison to CD. The inconsistencies you are noticing from your iPod are that some songs you downloaded from the internet were 192 or maybe even higher, while others are 128 or maybe even lower.

XM - XM, believe it or not, uses a maximum bitrate of 56kbit for the popular stations and even lower for talk/sports/etc. Note that this 56kbit is NOT MP3. Here we should have a little discussion about "codecs". MP3 is one type of "codec". Others include windows media (WMA), AAC (itunes music store), and TwinVQ (Transform-domain Weighted Interleaved Vector Quantization). XM uses a highly efficient codec called "aacPlus". Different codecs have different efficiencies. 128kbit aacPlus music will sound a LOT better than 128kbit MP3 Music. Since XM uses a 56kbit aacPlus stream, I'd estimate its performance would be comaprable to somewhere between a 96kbit MP3 and a 128kbit MP3 - which, overall, is pretty poor. That's why if you take an XM tuner and listen to XM with very high quality headphones, or on a high-fidelity home stereo, it sounds like pure crap. Sirius suffers from the same low sound quality. The reason is because of the bandwidth for XM and Sirius is limited. XM is allowed a 12.5MHz chunck of the 2.3-2.4GHz range.

Hope this clears up any confusion.

Adobeman

Well, I hear you BUT...
Most folks can hear well into the 15Khz range so if you use a "rule of thumb" that I recall from my engineering school (EE) days you need a 5X sampling rate to avoid huge errors/aliasing in wave form capturing. So, at 44K you will only get about 3 samples or less for anything in the 15KHz range. At 96K you will get more samples for the same content. Granted were not talking about that many samples (3 vs. 6 or so) but I have to believe that the roughly doubled amount of samples might be noticed on a very good system. Something well beyond what you will find in a car. I don't think it is something that is huge but rather a very, very subtle difference in imaging. As in how transparent, or real, the sounds are. I agree you won't hear it unless you are really concentrating on the sound and in the right listening spot for the room.

Higher sampling rates should also reduce the amount of smoothing that is required by any analog circuits on the output as well. Again, subtle stuff for sure.

Not looking to stir up a debate just commenting. Your right, I really would be lost getting back into DTFs, convolution, etc. That was a long, long time ago.

pohljm

I am not even going to attempt to disect this, but what you are essentially saying is that I should not be able to tell any difference in sound quality between cd and dvd-a? good theory perhaps, but easily dissmissed because I can easily hear a difference, funny thing is the best quality sound still comes from vinyl playing on my Linn turntable.

Desert_TL

That is incorrect. I said that you would not be able to tell the difference between a song sampled at 44.1khz and one sampled at 96khz. However, songs on a DVD-A are encoded with 6 channels of audio (5 "mains" plus a sub channel) whereas CDs are encoded with straight 2-channel stereo. The number of encoded channels has nothing to do with the sampling rate. However, the original post didn't ask about the difference in sound quality between DVD-A and CD, only CD vs. iPod vs. XM, which I addressed.

Desert_TL

False. The original waveform can be perfectly reconstructed by meeting the nyquist criterion. That is, if the highest frequency in the waveform is 20khz, then a 40khz sampling rate will exactly reconstruct the initial waveform. Of course, this perfect reconstruction is in the Fourier domain.

HOWEVER, in your defense: the nyquist sampling theory is valid ONLY when the single is perfectly bandlimited, and any signal that is timelimited can never be perfectly bandlimited. Additionally, the reconstruction process requires the use of ideal scaled and delayed sinc functions. In practice, it implies that each sample contributes to the reconstructed signal at almost all time points, requiring summing an infinite number of terms.

So, in conclusion, you are partially correct. Saying that the upper range of human hearing is about 15khz isn't bad. And then, considering that CDs are sampled at close to 45khz, the audio is already has 50% oversampling over the nyquist rate (3 samples per full period for the 15khz component). I would say, with full confidence, that even with the highest fidelity audio equipment ever made, you would be unable to distinguish between 44.1khz and 96khz sampled audio.

Another difference between DVD-A and regular CDs that nobody has mentioned, and is FAR more important than the sampling frequency is the number of bits per sample. On DVD-A, there are 24 bits per sample. On CD, there are 16 bits per sample. That means that on CD, there are 2^16 possible amplitudes for the sample, whereas on DVD, there are 2^24 possible amplitudes per sample. Thus the sampling sensitivity of DVD-A is 256 times higher than CD. Now, with VERY high fidelity home audio equipment (note: this does not include ANYTHING in any car ever made), the difference would be slightly noticeable.

Thus leaving the only real advantage to DVD-A being the ability to natively encode 6 channels instead of 2. That is what makes DVD-A sound magnificent.

Perhaps it is best to agree that psychology plays a far higher role in sound quality than any of these things. Remember when CDs first came out? There was a huge rumor that if you took a green marker and marked the outside edge of the disc green, the audio would sound noticeable purer and crisper. Of course, you and I know that that is a load of bull. But people who don't fully understand the underlying technology were quick to try it and 99 times out of 100, they would agree that it sounded better. It was purely psychological but it was amazing how well it worked.

evantec

I've found sometimes FM has better fidelity than XM! But given all the commercials these days, you only have 50-50 chance of getting music!

I agree that the pricing and number of channels is the key benefit of XM. Even if you have some great CDs or an iPod with 1000 tunes after awhile you get bored of your own music.

The comparisons elsewhere on this thread about the codecs are pretty interesting. I didn't realize XM often used a 56K codec.

If we're doing a comparison of low-quality channels, check out the Traffic Channels. Some of them are so compressed, they make the live voices sound like a speech synthesizer! I bet they're 8K or even 4K.

ChicoOG

Nice speaker selection...What kind of amp? I saw that stock opening set-up, it wasn't clean enough for my tastes, but I'm sure it is a huge improvement over stock...would the idmax sub work there?

What I understand from the debate so far, in laymans terms:

DVD-A is best, then
CD, then
iPod or XM

We have no control over XM quality, some stations are good, some are not. But I can influence the iPod (MP3) quality by downloading via LAME or a similar product and only downloading high quality (or highest kbits) possible.

Desert_TL

I know all of that was WAY more information than anyone ever wanted

Yeah, your best bet for iPod is to either downloaded them from the itunes music store (99 cents per track, AAC codec, 128kbps bitrate, roughly equivalent to a 256kbit mp3, that's pretty dang good quality, very near CD quality but there is still a noticeable difference, legal), or rip the songs yourself at high bitrate, or try redownloading them from another source.

On the comment on FM sounding better than XM. Just depends on the FM station. I used to be a chief engineer for a college radio station and when I took over, the sound quality of the broadcast was crap. They were using mostly 40 year old equipment and what new processing equipment they had, was configured improperly. I installed a new Harris transmitter and reconfigured the $5,000 sound processors they had. The processors are designed to make the FM broadcast sound as loud and clear as possible given the limitations of FM. The result sounded CD quality to me. Just depends on how well configured the station is and how expensive their hardware is. But yes, you aren't imagining things if you have heard FM stations come in better than XM

ChicoOG

It was more than I needed (or could digest), but it was definitely interesting...much appreciated

I've downloaded everything from itunes...yet have noticed inconsistency in sound/volume/eq/mastering levels/quality. I ran the entire library through their "sound enhancer", "sound check", and "equalizer" over the weekend. Everything sounds a lot better and is more consistent. Having everything in such a small package is very convenient...so, I am trying to squeeze out every drop of SQ I can from it.

Adobeman

Sounds good to me. Lots of cobwebs in my brain about this stuff for sure. So given a 15K square wave (or any non sinusoidal) what happens to the non-fundamental harmonics that fall above about ~22K, which is all of them. I seem to remember that they will be aliased as lower frequencies in the sampling. Or is that what you were getting at with "signal is perfectly band limited" (like a steep filter to eliminate anything above the sampling-frequency/2 ?). Seems that none of the harmonics would get sampled essentially leaving you with the 15Kprimary as a sine wave. But seriously, what possible real world example could this be. Even my most eccentric and bizarre "art" friends don't listen to isolated 15K square waves. Again... I think we agree that none of this plays a rat's ass....

I agree completely about the psychology factor. Your brain will very easily convince you that something sounds better if you "think it should" or "want it to" sound better. Plus a true comparison would be difficult for most to set up. Who has the exact same content mastered at 2ch 96/24 and at 2ch 44.1/16 ? and can play it on the same system in a "blind test". Certainly well under 0.5% of the population, that cares, if even that. I know I can't set it up.

Now if you really want to stir up a "fun" thread to watch start one about the audible differences $100 optical/toslink cables can make in the sound Sheesh !

Hi There

You forgot the errors in amplitude inherent in real-world digital sampling. I don't know why they never mention that when discussing nyquist. Fact is, there are an infinite number of signals that will fit the nyquist-rate-obeying samples, due to the fact that every digital system I know of has discrete amplitude scaling as well as discrete time sampling, even given a perfect sinc (which is a difficulty in and of itself). Even if you're perfectly scaling the sincs to match what they're given, they're still being given an imperfectly scaled signal.

Of course, all this is kinda moot. Even if a human being could tell the difference between sampling at CD quality and DVD-audio quality, you're still running the signal through speakers that are nowhere near accurate enough to differentiate the two. Any percieved differences between the two are likely caused by the presence of additional channels, differences in the mastering process (noise reduction, equalization, etc. done by the studio for the DVD-A re-release), and placebo effect. Speakers, although exhibiting astonishing levels of engineering, are still the weakest link in modern audio reproduction technology. Some miniscule differences in frequency response on the output from a given DVD-A just doesn't stack up to the differences in response on a given speaker.

Edit: didn't read the response above. Agree about the $100 cables, they make me laugh (but people will actuall argue in their defense?).

Desert_TL

If you will read my post above, I believe I addressed this issue. You and I may be thinking about different things though:

I think there is one thing we can all agree on here though, and that is that people who buy Monster cables thinking that they will noticeably improve their sound quality deserve to lose their money. At least for cables that carry a digital signal (like optic cables). Even the value of Monster cables for analog signals is dubious at best. Electromagnetics is a black art and it would be extremely difficult to prove that monster cables don't make the sound better (even something as simple as the electric field momentum in dielectric media is disputed; I happen to think that the momentum is actually a geometric average of the Minkowski and Abraham forms, but I guess that's a topic for another time). But I happen to fully believe that any perceived difference in sound quality from monster cables is purely psychological, but hey, if you want to waste your money, go for it. Makes me feel like I'm in the wrong business. I could buy bulk 2 gauge copper wire for 12 cents a foot wholesale, wrap it in a fancy looking package, say it has "superior sound quality" and charge $100 for 6 feet too

Hi There

I think so. I was addressing the sampling of the analog signal (discrete in time as well as amplitude), I think you were addressing the errors in reconstruction due to having an infinite summation of the effects of each sample on the reproduced signal and ideal low-pass filtering...even given a "perfect" reproduction based on the information the DAC's are given, the information handed to the DA process is discrete in amplitude as well as time, so you have more avenues for error in reconstruction than most signals professors address.

But we're splitting hairs. Speaker quality/enclosure/location/aiming/environment is/are the major sound-killing issues left to be addressed in car audio is all I wanted to say...the rest of the problems (amplification, digital processing/time alignment, etc.) are all about some small fraction of the overall hifi experience ( important considerations, no doubt, but still not the major "bug" in the program...). Low-bitrate mp3 and satellite radio both knowingly sacrifice audio quality for portability/expanded choice, so I don't address them in a fidelity discussion except to say they're not about fidelity.

I will say this: XM does sound slightly better than Sirius to my subjective ears. Sirius seems to push a little harder when it comes to compression. In Sirius' defense, there is no way to make Oprah sound good. That, and I can point to many experiences in FM listening that are far superior to any sound that has come out of either of my satellite experiences.

Hi There

Well, I have my doubts about that as well...It's hard for me to believe that the mechanics of a given tweeter (even less so a woofter) would be sensitive to anything like a 1/(2^16) shift in amplitude, considering they're likely in the process of moving back and forth and have their own momentum/inertia to overcome. Even given that, I doubt my ears would be sensitive to the shift, which could happen in either direction (higher than or lower than) for a given signal, and which, I would think, would average near to 0 over the, say, 15000 oscillations the tweeter is producing every second. That, and wouldn't that result in, overall, a 1/(4Pi X 2^48) change in overall power? My eyes can't tell the difference if I rotate the knob on my dimmer switch 1/(2^16) rotations, I don't know why my ears would be any better at it.