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WCBS FM Audio

David Reaves said:
I have a pretty strong opinion about this: There is not and has never been any point in asking radio/audio listeners about quality! Generally speaking, they do not think about it, never mind talk about it. More often than not, they react on a primitive basis, impulsively and subconsciously. As with any animal, one can be expected to instinctively move away from pain or discomfort, and towards pleasure or potential pleasure, whether they are cognizant of the action or not.
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And the degree of "pain or discomfort" has a lot to do with the nature of distortion added through processing (and other parts of the air chain).

For example, most AM stations can get by with asymmetrical modulation as a loudness-boosting technique because the added distortion is primarily even-order harmonic, the same type that occurs naturally in the human ear at moderately loud volumes. We encounter this on a daily basis, so when it occurs in processed audio (at reasonable levels) we don't really notice. In fact, some will say it adds warmth to unprocessed sound.

However, aliasing distortion lacks a natural harmonic relationship -- the products are "folded back" at the Nyquist frequency -- so it becomes very conspicuous.

I react much the same way to the artifacts of low-bitrate codecs, such as the one used for AM HD Radio. The system's measured distortion (with steady state tone as the source) may look OK on paper, but there's something going on there with voice and music that just doesn't sound natural.
 
My experience is that in order to stand listening to audio I need a minimum of 48 kbps using AAC+, with NO parametric stereo. 64 Kbps is much better sounding then 48 though.

With MP3, I can BARELY stand 96 kbps. 128 sounds okay on about 2/3's of the stuff, 160 on about 85% of it.

WMA just sounds awful to me no matter what the bit rate is. I don't know why, but it gives me a headache.

I'm not listening on a super great system now either. I have an M Audio Delta 196 card and a modified Sonic Impact original T amp (5 watts per channel). Speakers are these Insignias: http://www.bestbuy.com/site/olspage.jsp?skuId=7705307&type=product&id=1138085354138
 
In my opinion, the best bitrate/quality compromise for HE-AAC=AAC+=aacPlus is 48 kbps. Lower than that the artifacts are more pronounced, higher than that and the artifacts don't get significantly less reduced. Sometimes (for mobile streaming, for example) you need to go to 32 kbps, but IMO 48 kbps is the ideal bitrate for HE-ACC.

However, although HE-AAC at 48 kbps sounds best of all other codecs, that does not mean it sounds excellent. Again, it's the best codec for very low bitrates, but the sound quality is a compromise. It does have wide frequency response at the expense of metallic and gritty high-end, due to the artificial nature of SBR technology.

At 96 kbps, AAC outperforms it by a mile! In HE-AAC only the low band is coded with AAC, while the high band is synthesized, whereas in AAC the whole spectrum is codec with AAC. That does not work so well at very low bitrates (64 kbps stereo and below), but at higher bitrates (96 kbps and higher) it works much better than the AAC plus SBR synthesized high band combination. At 128 kbps, AAC was found to be transparent in EBU testing and it indeed sounds excellent (for final transmission coding; as always keep your sources uncompressed!).

To summarize, for streaming I would advise:

<= 64 kbps ---> HE-AAC (v1 seems to be just as good as v2, despite marketing claims)
>= 96 kbps ---> AAC


Regards,
Goran Tomas
 
Fellow audiophile and sometimes-poster JesseG explained that anything below 40kbps AAC+ is PS-AAC or V2 which adds Parametric Stereo. Anything between 40kbs and 80kbs is HE-AAC V1 without Parametric Stereo. Things above 80kbps is LC-AAC, which is low complexity. Heck let me just quote Wikipedia:

High-Efficiency Advanced Audio Coding (HE-AAC) is a lossy data compression scheme for digital audio. It is an extension of Low Complexity AAC (AAC LC) optimized for low-bitrate applications such as streaming audio. HE-AAC version 1 (HE-AAC v1) uses spectral band replication (SBR) to enhance the compression efficiency in the frequency domain. HE-AAC version 2 (HE-AAC v2) couples SBR with Parametric Stereo (PS) to enhance the compression efficiency of stereo signals. It is a standardized and improved version of the AACplus codec.
 
Timmy said:
Fellow audiophile and sometimes-poster JesseG explained that anything below 40kbps AAC+ is PS-AAC or V2 which adds Parametric Stereo. Anything between 40kbs and 80kbs is HE-AAC V1 without Parametric Stereo. Things above 80kbps is LC-AAC, which is low complexity. Heck let me just quote Wikipedia:
Click to expand...

No, it doesn't work that way. There are three separate codecs:

1) AAC (LC profile is typcially used in streaming, but there are others)
2) HE-AAC (aka aacPlus or AAC+), which is AAC + SBR (spectral band replication)
3) HE-AAC v2 (aka Enhanced HE-AAC, aacPlus v2 or eAAC+), which is AAC + SBR + PS (parametric stereo)

You have to choose one that you will use within a particular stream. There is no automatic switching between AAC, HE-AAC and HE-AAC v2. Unless someone made a propreitary encoder-decoder combination that does that sort of scaling on the fly, but I'm unaware that someone did. And if it did, it would be only work with that encoder-decoder combination. Thinking about it, for such thing to happen, there would have to be some kind of bi-directional exchange between the encoder and the decoder to negotiate which codec to use. Or (how it's usually done), you simply have a multiple separate streams (each encoded with different codec and bitrate) and then a decoder (player) can switch between them on the fly, depending on the network congestion and conditions. But that's a client side stream switching. You still have to have as many separate encoders with different codecs and bitrates on the encoding side.


Regards,
Goran Tomas
 
I agree that HE-AAC only makes sense up to 64kbps - even at 80kbps AAC is far superior!

I cringe when I see Netcasters doing silly things like using 96kbps / 128kbps HE-AAC or even higher bitrates. The codec should really only have options up to 64kbps and then switch to pure AAC above that bitrate otherwise the resulting quality is worse!
 
BofH said:
I agree that HE-AAC only makes sense up to 64kbps - even at 80kbps AAC is far superior!

I cringe when I see Netcasters doing silly things like using 96kbps / 128kbps HE-AAC or even higher bitrates. The codec should really only have options up to 64kbps and then switch to pure AAC above that bitrate otherwise the resulting quality is worse!
Click to expand...

Yes, you're absolutely right!

I think problem is that because of the marketing behind HE-AAC and commercial HE-AAC encoders, a lot of the people got an impression that it is the best codec per se. Regardless of the application, bitrate, etc. They simply miss or ignore the part where it says for _very low_ bitrates.


Regards,
Goran Tomas
 
It's Compellors and Orban 1100PC. The bitrate of the stream is determined by the DMG, which takes care of the stream once it leaves our building.
 
erwin33 said:
Ok, thanks. But why is the output audio on the Fresh FM stream so soft? I must turn my volume up to hear something.
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Probably because the source material isn't hypercompressed! It is from back when the mastering was done properly!
 
No, don't think that's the problem here. The whole output sounds to soft in volume, check it and than the audio from CBS FM for example you hear the difference. CBS is louder.
 
Fresh is processed for high TSL and the audio matches that of most of the other AC stations. CBS FM is a statement, a sound larger than life for a station that is. Although, I do have to make an adjustment... it seems the audio may have changed a wee bit with the installation of a new exciter this week.
 
In a yet to be published research shows that 12% of all radio listening time in the Netherlands is done over the internet. The figures in the research also shows that in the UK this is "only" about 2.2%. Not sure how the numbers are in the US but it proves that streaming in good quality is a real thing to consider. Do you wait for people to ask for better quality or do you offer good (comparable to FM) quality and extend your potential to reach out to new listeners?
 
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