Music Choice Channels- Are they really CD quality? - AVS Forum
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post #1 of 9 Old 01-31-2008, 12:04 PM - Thread Starter
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I have a question about digital music channels for anyone who can answer- I listen to Music Choice channels on my cable box (hooked up to my receiver via HDMI) and the receiver recognizes them as Dolby Digital 2.0. I am curious whether this is a very lossy encoding of the music, or if it is true CD quality audio? Seems unlikely that it would be decoded to the same quality as the PCM on a CD. I searched the net for an explanation of the bitrate afforded each channel in a dolby digital 2.0 stream, and to try to find out if it decodes to the same quality as CD audio, to no avail. Can anyone shed some light?
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post #2 of 9 Old 01-31-2008, 12:44 PM
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This was discussed here a couple of months ago. Hope this link helps: http://www.avsforum.com/avs-vb/showthread.php?t=942404

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post #3 of 9 Old 01-31-2008, 01:17 PM - Thread Starter
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Ok, so according to the information in that thread, it looks like the audio is encoded to Dolby Digital 2.0 at a bitrate somewhere between 128 and 192kbps. What would this mean for the decoded output in terms of subjective quality when compared to, say a 128Kbps MP3 or a CD? I was under the impression that AC-3 is less efficient than MP3 in terms of subjective quality at the same bitrate- is my assumption correct? If so, that would mean that the audio on some of the Music Choice channels is actually below CD quality?

Doesn't seem right- Music Choice advertises CD quality audio. I realize this is a bit of a subjective discussion of the merits of AC-3 as a digital music playback medium, but I would think they would shoot for at least CD quality. Can anyone clear this up further?
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post #4 of 9 Old 01-31-2008, 02:25 PM
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I found this comparison of some different data rates and what they list for CD. It would seem that the figures quoted in that other thread would be "similar" to CD.

Quality Sample Rate Bits per Mono/ Data Rate Frequency
(KHz) Sample Stereo (Uncompressed) Band
--------- ----------- -------- -------- ----------------- ------------

Telephone 8 8 Mono 8 KBytes/sec 200-3,400 Hz

AM Radio 11.025 8 Mono 11.0 KBytes/sec

FM Radio 22.050 16 Stereo 88.2 KBytes/sec

CD 44.1 16 Stereo 176.4 KBytes/sec 20-20,000 Hz

DAT 48 16 Stereo 192.0 KBytes/sec 20-20,000 Hz

-------------------------------------------------------------------------------

Sorry, can't figure how to straighten out the table headings; hopefully it makes sense. Just trying to point out the CD data rate (uncompressed) of 176.4 KBytes/sec listed. I would love to hear from someone more knowledgeable than me about this!

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post #5 of 9 Old 01-31-2008, 04:07 PM - Thread Starter
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Quote:
Originally Posted by DocCasualty View Post

I found this comparison of some different data rates and what they list for CD. It would seem that the figures quoted in that other thread would be "similar" to CD.

Quality Sample Rate Bits per Mono/ Data Rate Frequency
(KHz) Sample Stereo (Uncompressed) Band
--------- ----------- -------- -------- ----------------- ------------

Telephone 8 8 Mono 8 KBytes/sec 200-3,400 Hz

AM Radio 11.025 8 Mono 11.0 KBytes/sec

FM Radio 22.050 16 Stereo 88.2 KBytes/sec

CD 44.1 16 Stereo 176.4 KBytes/sec 20-20,000 Hz

DAT 48 16 Stereo 192.0 KBytes/sec 20-20,000 Hz

-------------------------------------------------------------------------------

Sorry, can't figure how to straighten out the table headings; hopefully it makes sense. Just trying to point out the CD data rate (uncompressed) of 176.4 KBytes/sec listed. I would love to hear from someone more knowledgeable than me about this!

Okay, I think there's a better way to phrase my question. Let me explain.

176.4 KBytes/sec * 1024 = 180,633.6 Bytes/Sec
180,633.6 Bytes/Sec * 8 Bits/Byte = 1,445,068.8 Bits/Sec
1,445,068.8 Bits/Sec / 1000 bits/kilobit = 1,445.0688 kilobits/sec or kbps

So the bitrate in kbps from a CD would be : 1,445kbps

Please note:
KiloBytes (KB) and kilobits (kb) are not the same. The capital K means a multiplier of 1024 (versus 1000 for lower case k), and the capital B is bytes (8 bits).

Notice that the figure quoted in the other post that you pointed me to, makes
reference to the music being transmitted via Dolby Digital 2.0 at a compressed bitrate of between 128kbps to 192kbps. Comparing these numbers to the figure I calculated above, the compressed bitstream is transmitted at a bitrate that is about 1/10th of the bitrate of the original CD content. It's heavily compressed- so how much quality are we losing, relative to the original CD content, to achieve that compression?

My question is whether Dolby Digital 2.0, (the transmission format used by Music Choice) offers cd quality audio at a bitrate of 128-192kbps.

From what I've read, AC-3 was created around the same time as MP3 (1990-1991), but I don't know how comparable they are as far as compression efficiency versus subjective audio quality.
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post #6 of 9 Old 01-31-2008, 04:24 PM
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Quote:
Originally Posted by deecee20 View Post

Okay, I think there's a better way to phrase my question. Let me explain.

176.4 KBytes/sec * 1024 = 180,633.6 Bytes/Sec
180,633.6 Bytes/Sec * 8 Bits/Byte = 1,445,068.8 Bits/Sec
1,445,068.8 Bits/Sec / 1000 bits/kilobit = 1,445.0688 kilobits/sec or kbps

So the bitrate in kbps from a CD would be : 1,445kbps

Please note:
KiloBytes (KB) and kilobits (kb) are not the same. The capital K means a multiplier of 1024 (versus 1000 for lower case k), and the capital B is bytes (8 bits).

Notice that the figure quoted in the other post that you pointed me to, makes
reference to the music being transmitted via Dolby Digital 2.0 at a compressed bitrate of between 128kbps to 192kbps. Comparing these numbers to the figure I calculated above, the compressed bitstream is transmitted at a bitrate that is about 1/10th of the bitrate of the original CD content. It's heavily compressed- so how much quality are we losing, relative to the original CD content, to achieve that compression?

My question is whether Dolby Digital 2.0, (the transmission format used by Music Choice) offers cd quality audio at a bitrate of 128-192kbps.

From what I've read, AC-3 was created around the same time as MP3 (1990-1991), but I don't know how comparable they are as far as compression efficiency versus subjective audio quality.

Did you ever download MP3's? They run from 96kbps to 320kbps. Try downloading an MP3 of the same song from as low as 96k to as high as 320k. There you will get a better idea of what the compression sounds like.

CD's are uncompressed PCM modulated audio at 1444kbps. Mpeg compression can really knock that down to 1/10th of the size. Rip a CD track to a WAV file, then rip the same track to a MP3 file. Look at the size difference. Then play both one at a time and see how it sounds.
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post #7 of 9 Old 01-31-2008, 04:42 PM - Thread Starter
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Quote:
Originally Posted by cypherstream View Post

Did you ever download MP3's? They run from 96kbps to 320kbps. Try downloading an MP3 of the same song from as low as 96k to as high as 320k. There you will get a better idea of what the compression sounds like.

CD's are uncompressed PCM modulated audio at 1444kbps. Mpeg compression can really knock that down to 1/10th of the size. Rip a CD track to a WAV file, then rip the same track to a MP3 file. Look at the size difference. Then play both one at a time and see how it sounds.

I understand that MP3 offers about a 10:1 compression ratio while still maintaining roughly CD quality sound. I'm asking whether AC-3 offers the same, better, or worse. I'm tempted to believe it's better, but I've read and heard mixed information on that. That's why I'm asking.

Also, you can easily make the argument that MP3 at ~128kbps does a poor job of maintaining the nuances of CD audio. If you're playing Mp3's versus CD's over a full-size listening setup versus a boombox, there is quite a difference, so I'm not sure you can draw a parallel between MP3 and Dolby digital.

All I'm trying to figure out is what the quality scale is for Dolby Digital at different bitrates. If it's better than MP3 at the same bitrates, then the claims that Music Choice makes about CD quality audio would be correct. Again, I suspect that they are, but I've heard mixed information on the efficiency of Dolby Digital when compared to other popular audio codecs. There's a lot of information comparing the efficiency of MP3 to AAC to OGG, etc, but very little out there that talks about the effectiveness of Dolby Digital's compression for high quality 2-channel music listening.
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post #8 of 9 Old 01-14-2013, 01:35 PM
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I was wondering this with my new AVR's better Dolby processing, and a search led me back to this forum/this thread. Do digital music channels use when possible remastered, SACD, or other versions of songs that are superior to CD versions? Because sometimes the songs I hear on Music Choice sound better than the same songs that I have on CD.
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post #9 of 9 Old 01-15-2013, 02:16 AM
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Quote:
Originally Posted by deecee20 View Post

All I'm trying to figure out is what the quality scale is for Dolby Digital at different bitrates. If it's better than MP3 at the same bitrates, then the claims that Music Choice makes about CD quality audio would be correct.
Extensive tests were carried out as reported here. Fig 1 shows the essential results.



MP3, a.k.a. "L III" is more efficient than DD at 128 kbps. But if the DD bitrate is 160 kbps or higher, the quality is better than MP3 @ 128 kbps. Dolby encoders default to 192 kbps for stereo, but that can be overridden. Is there any way to confirm what MC is actually using? Maybe it varies based on the channel genre?

Be advised that these are results from 14 years ago. The encoders may well have improved since then.
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