A few questions before I transcode my entire flac collection to aac

[dave_in_gva]

Hi,

I'm a new user very happy with dbPoweramp Reference (v 12).

I've used it to rip my entire CD collection and now have about 60 gigs of flac files.

The family uses ipods (generations 2 through 5) so I now want to use the batch converter to convert the flac files to aac files.

I've done a brief test to see how the batch transcoder works and everything worked fine with 40 or so test files. Along the way I saw a couple of options where I was not sure what to select so I thought I'd post three questions here for the best way to do the transcoding job before I begin.

1. My first question is whether I should select VBR or CBR and what other options I should select. I want to end up with files for the iPod at about 224 kb/s in terms of file size and sound quality. I'd be very grateful to anyone who can give me a short, straight answer on what options I should be selecting to retain as optimal as possible sound quality from my flacs and get me to about this file size in aac.

2. My second question concerns ReplayGain. I used RPG during the original ripping of my CD collection, so I have this info for each track and ideally of course I would love to have the transcoding use this data to give me aac tracks that all play at the same volume through an iPod. I've read a recent post that seems to indicate that if I download and utilize another DSP (the volume normalize DSP), that it can do this. Unfortunately it is not stated explicitly in the other thread what options or buttons I should click on within the volume normalize DSP to do this - there is a choice for ReplayGain within the volume normalize DSP but there is also a post saying the DSP help file says this choice does NOT use tags and instead physically changes the file. It may be this is what I want as I know that ReplayGain inserts parameters that are afterwards used by Foobar etc. and I would now be wanting to prep the file for playback over an iPod, but still it would seem to me that I would WANT the volume normalize DSP to use the tag info (originally generated by RPG when I first ripped the CD) and then go ahead and physically change the file during the transcoding to get all tracks sounding more or less at the same volume level. Can someone steer me straight on exactly how I should be using the volume normalize DSP during the transcoding?

3. Finally, my plan was to batch the entire 60 gigs in one operation (that would last around 24 hours on my system). I have seen other posts where people mention using the test conversion (no write) option to search for problem files so the conversion is not stalled. Would this be a good idea and how long would it take to run the test conversion (no write) on 60 gigs of flac files? If it's a short (e.g. less than 15 min) operation and quick insurance the whole process will not get aborted along the way I am up for it. If running a simulation on 50 gigs of files would itself take an hour or more I'd probably just go straight to the real run. Comments on this welcome, including whether as an alternative I should divide the transcoding up into 3 or 4 runs of 15-20 gigs.

Best,

Dave M

[LtData]

Re: A few questions before I transcode my entire flac collection to aac

1. For about 224kbps, I believe you need to pick VBR .55 or .6.

2. I'm not sure if the "Volume Normalize" ReplayGain options uses the RG tags if they are already there or just re-calculates the data for the file. As for if this is what you want to do for the iPod, yes, you need to change the file so that the iPod will play the altered file.

3. Regarding transcoding large batches of files, as long as you are not deleting the source files, you should be fine to just let it run. However, it would probably be a good idea to do a rest run on a few (50-100) files to make sure no obvious problems preset themselves. Personally, I have re-encoded my entire library in one shot before and it takes about 2-2.5 hours to do all of it.

[Spoon]

Re: A few questions before I transcode my entire flac collection to aac

Volume normalize will always recalculate the ReplayGain before normalizing, on a fast computer it only takes a second or so.

[TechVsLife]

Re: A few questions before I transcode my entire flac collection to aac

Consider using aacGain:

http://forum.dbpoweramp.com/showthread.php?t=13277

Volume normalize will always recalculate the ReplayGain before normalizing, on a fast computer it only takes a second or so.

I assume any ReplayGain tag gets removed if it is actually physically applied (I mean if the track audio data gets altered in normalization)? excuse me if I'm still confused about the process.

[Spoon]

Re: A few questions before I transcode my entire flac collection to aac

Yes we always drop the RG tags on transcoding

[LtData]

Re: A few questions before I transcode my entire flac collection to aac

Note that dropping RG tags on transcoding is done due to the fact that the RG values will differ depending on the codec used to compress the file, especially regarding lossy codecs.

[TechVsLife]

Re: A few questions before I transcode my entire flac collection to aac

Even without transcoding, I assume the RG tag removal should also be done by any program that has applied the RG tag info to alter the audio data (rather than just calculating the RG and adding a tag), to avoid having a later program use a mistaken double adjustment.

I found that the correct aacGain website seems to be:

http://altosdesign.com/aacgain/

Note that dropping RG tags on transcoding is done due to the fact that the RG values will differ depending on the codec used to compress the file, especially regarding lossy codecs.

[dave_in_gva]

Re: A few questions before I transcode my entire flac collection to aac

LtData, Spoon and TechvsLife,

Thanks very much. Tech I read the threads you linked to re aacgain. I'm attracted to the idea that the gain adjustment is a better method than peak normalization. I am not sure if the volume normalize DSP available for dbPoweramp is using peak normalization or some more advanced method.

I'd be happy to use aacgain instead of the volume normalize DSP if it was possible - unless Spoon or someone says the volume normalize DSP is using as sophisticated a method.

If I do this I assume I would need to do it outside of my batch conversion using dbpoweramp Reference, correct? I do not see aacgain listed in the DSP effects available to Reference so it looks as if it has not been integrated even if as you say it is no longer beta.

So I suppose the process would be to simply transcode to aac using the parameters proposed by LtData and without using the volume normalize DSP and then run aacgain on the aac files created. Is this right?

Best,

Dave M

[TechVsLife]

Re: A few questions before I transcode my entire flac collection to aac

Yes, you wouldn't want to normalize with the dMC option AND also use aa3gain, but do one or the other. I haven't started using aacgain myself, but I know that the author (Dave Lasker) and other users post on the ha forum, so you can ask questions about it there. I believe that there is also a GUI frontend that can be used with it:

http://www.hydrogenaudio.org/forums/index.php?showtopic=55545

[Spoon]

Re: A few questions before I transcode my entire flac collection to aac

Our normalize comes in 3 flavors:

Simple Peak
Replay Gain
Adaptive - argubly better than replay gain in noisy environments as instead of a single gain value that peak, replaygain and aacgain / mp3gain would use, the gain is calculated 1000's of times in the file.

[dave_in_gva]

Re: A few questions before I transcode my entire flac collection to aac

Thanks again Spoon. So just to be clear, these 3 flavours you refer to (Single Peak, RPG, Adaptive) are all available to the user through the Volume normalize DSP?

If this is correct I'll use that as I can do it on the fly with the batch transcoding. And from what you describe I'll use the Adaptive option.

Best,

Dave M

[LtData]

Re: A few questions before I transcode my entire flac collection to aac

Correct, all three flavors of normalize he mentioned are done by the "Volume Normalize" DSP.

[TechVsLife]

Re: A few questions before I transcode my entire flac collection to aac

I'm not at all sure about this, but it appears that "adaptive normalization" would introduce the risk of distorting the relative volumes within a track. If a track has a low section, followed by a very high volume section, then might not adaptive normalization change the relative volume of the sections to one another? (versus replaygain or mp3/aacgain, which I believe lowers or raises the volume of the whole track, so the relative volume of sections within the track doesn't change).

(The third kind of normalization, simple peak, would also seem to change the relative volume within the track.)

Our normalize comes in 3 flavors:

Simple Peak
Replay Gain
Adaptive - argubly better than replay gain in noisy environments as instead of a single gain value that peak, replaygain and aacgain / mp3gain would use, the gain is calculated 1000's of times in the file.

[LtData]

Re: A few questions before I transcode my entire flac collection to aac

From the DSP help file in the Volume Normalize section:

There are 4 different ways of adjusting the volume of an audio track:

* Peak to Peak: simplest volume normalize, the peak (or maximum) value is found and the whole track volume is adjusted so that peak touches the desired volume,
* ReplayGain: a more advanced normalization, the average loudness is calculated and the volume is adjusted. This method does not use ID Tags to store ReplayGain values, rather the audio is adjusted. If a Replay Gained track is played next to a non-Replay Gained track, it will sound quieter, as Replay Gain requires head-room to prevent clipping.
* Adaptive: the best way to describe adaptive, is like having your hand on the volume knob, constantly adjusting it up and down (a window is used to detect loudness) to compensate for quiet parts, ideal for creating a track to play in a noisy environment (such as car).
* Fixed Amplification: Amplifies the audio by a fixed amount, +6 dB is x2, where -6 dB is divide by 2, be careful not to clip audio (go over the maximum).

[EliC]

Re: A few questions before I transcode my entire flac collection to aac

Yes we always drop the RG tags on transcoding

Why use any CPU time if its already calculated?