FLAC conversion is very slow

[curiousMonkey]

I am converting about 2800 files (24/48) from AIFF to FLAC using the default setting (5).
The encoding speed is only 3.4x and the estimated completion time is 52 hours, although dMC is using 8 cores.
I know that my original conversion from WMA lossless to AIFF was much quicker and that CPU utilization is almost zero.

Can anyone explain why the process is so slow?

[curiousMonkey]

Re: FLAC conversion is very slow

I restarted the process because I noticed that the directory structure being created was incorrect.
When the second run started the encoding speed was 300x but it has quickly dropped to 18x after a few minutes.
Once again I see that CPU utilization is almost zero.

[Spoon]

Re: FLAC conversion is very slow

If a network is involved then that is likely the slow part.

[curiousMonkey]

Re: FLAC conversion is very slow

There is no network involved. I have tried using a single drive and two different drives.
Something seems to be blocking the conversion when is FLAC. The conversion speed was about 120x when I used ALAC.

I also noticed that conversion to WAV does not use multiple CPUs.

[Spoon]

Re: FLAC conversion is very slow

CPUs are not required when converting to wave as there is nothing for the CPU to do (no encoding).

When encoding FLAC you are best having only 1 cpu encoder, because the CPU is faster than the HDD can supply the data, and reading from 8 aiff files at the same time will incur a seek time, so try the DSP effect 'Multi-CPU Force' set to just 1 cpu.

If you have SSD drives then seek time is not a problem.

[curiousMonkey]

Re: FLAC conversion is very slow

I ran another test while watching the task manager and had my speakers enabled.
The CPU utilization starts at about 85% and then drops in steps to 60, 50, 30 and then 1%.
I can hear some beeps as the CPU drops, is there any error information logged that can be reviewed?

I checked the process list and see the multiple threads created for each CPU.
They are all idle.

This all seems strange to me because I had no problems converting WMA to AIFF even when the source directory was on my network.

[Spoon]

Re: FLAC conversion is very slow

Run the Program 'Resource Monitor'

and look on the Disk tab, it is likely the disk which is the bottle neck, not CPU.

Also it is important you test encoding on 1 cpu only.

[bhoar]

Re: FLAC conversion is very slow

Run the Program 'Resource Monitor'

and look on the Disk tab, it is likely the disk which is the bottle neck, not CPU.

Also it is important you test encoding on 1 cpu only.

Possible the disk queue is full and/or main memory write cache is getting saturated? But why only with FLAC and not with ALAC? Is there something in the chain causing more I/O to the FLAC file than to the ALAC file? Something about the tag write process? Or maybe something else on the system changed...

Brendan

[curiousMonkey]

Re: FLAC conversion is very slow

With only one CPU, the encoding speed is around 63x after 6 minutes.
The encoding speed has been slowly decreasing, it started at about 75x.

The estimated completion time is 2 hours 40 minutes.

[curiousMonkey]

Re: FLAC conversion is very slow

I switched to 2 CPUs and the encoding is over 77x after 25 minutes

[Spoon]

Re: FLAC conversion is very slow

It was the seeking of HDD which was killing the speed.

[Michael Sargent]

Re: FLAC conversion is very slow

Are you using USB 2.0 external drives?

They can be pretty slow at times. I highly recommend USB 3.0.

Mike