Thread: What.CD interview: TIPS and TRICKS

Some tips for those who are trying to get into What.CD via the interview process.

1. You will be asked some personal information at the beginning, e.g. where do you live, your e-mail, possibly your nationality, and additional different crap just to disturb your privacy.
2. Since the What.CD is very concerned about lossy format uploads (along with lossless), they want to make sure you understand lossy formats. You basically need to learn to distinguish lossy format names from lossless format ones.

The lossy formats:

mp3;
AAC (can be called MP4) – is successor of MP3;
(Ogg) Vorbis - (Vorbis commonly used inside Ogg container);
AC3 - multichannel music compression technology developed by Dolby Laboratories;
DTS - Digital Theater Systems.

Most likely you will be asked to answer questions related to mp3 only. In particular, LAME is the What.CD recommended encoder to transcode between lossless and lossy formats. Make sure you remember which bit rate is higher of which:



-b 320 (CBR) > -V0 (~245 kbps=220-260) > -V1 (~225 kbps=190-250) > -V2 (~190 kbps=170-210) > -V3 (~175 kbps=150-195) > -V4 (~165 kbps) > -V5 (~130 kbps) > -V6 (~115 kbps).

Know how to explain in your own words the following abbreviations: ABR (Average bit rate), CBR (Constant bit rate), and VBR (Variable bit rate). Make sure you know what differences are between those (in short).

Know the lossless formats:

ALAC (Apple Lossless Encoder);
FLAC (Free Lossless Audio Codec);
WAV – RIFF container most frequently containing PCM;
APE (Monkey's Audio) - main competitor for FLAC;
WavPack - free open source lossless audio compression format developed by David Bryant;
Linear Pulse Code Modulation (LPCM or just PCM) – never compressed.

Do not get trapped with question like “Which of the following transcodes are acceptable by the what.cd transcode rule? (they frequently will give the “rule” before the questions). Just know that ONLY LOSSLESS TO LOSSLESS and LOSSLESS TO LOSSY transcodes are allowed there. You are not allowed to transcode Lossy to lossy format ever!

Real examples are as follows:
CD -> V0 -> FLAC - NO
CD -> WAV(PCM) -> FLAC - acceptible
CD -> MP3 320(CBR) -> MP3 320(CBR) - NO
CD -> V2 -> FLAC - NO
CD -> APE -> FLAC - acceptible
CD -> MP3 V0(VBR) -> MP3 V2(VBR) - NO
CD -> Ogg Vorbis q10 -> FLAC – NO

Something like that!
More to come.



Part II

From whatever has been explained above, please try to provide correct answer to the following questions (questions are based on previous real situation). Please note, I am not a member of What.CD. The tutorial though contains real examples that have been previously used during various interviews and kindly provided by those interviewed.

Introduction:
1. Have you ever had an account at What.CD?
2. Have you ever been interviewed for What.CD before? If yes, who was your interviewer? What was your nickname?
3. Why do you want to join What.CD?
4. How often do you plan to visit the site?
5. Are you at home at the moment? Where are you living?
6. Where did you learn about What.CD? If this was online, please give me a link.
7. Have you ever sold or traded invites? If you admit to it now you will be forgiven, but if you lie and I find out later you will lose your account!
8. What is your email address?
9. Is English your first language? If not, what language is?
10. Do you have any experience in making torrents?
11. Are you on any other private torrent sites? Please list them.

Note: Please always consider your privacy while choosing to answer the questions. Sometimes, you may even not to know to what results it may lead at What.CD.

Some of the questions:
1. What is the expected (or target) bitrate of V0 and V2 presets, or the range of V0 and V2 presets?
2. What is the difference between a VBR and CBR file, and which one do you prefer?
3. What is LAME?
4. What is a transcode?
5. What does 'lossless' mean when referring to file formats? Also, what does 'lossy' mean?
6.
a. Are lossless to lossy transcodes allowed?
b. Are lossy to lossy transcodes allowed?
c. Are lossy to lossless transcodes allowed?
d. Are lossless to lossless transcodes allowed?
7. Identify the following as either a lossy or lossless format :
a. Ogg Vorbis
b. APE
c. WAV
d. mp3 320
e. FLAC
f. V2
8. Please rank the following in order from highest to lowest bitrate :
V0
V2
FLAC
WAV
AAC 320
mp3 192 CBR

More to come.



Part III

Next thing that you may encounter during the interview is spectral analysis of the audio files (this seems to be not always the case). Still, you should be prepared to recognize quality lossless wav file as opposed to lossy mp3.

Should you have problem in performing the task, this seems to not always be a reason to fail you. You will be provided a sample image with spectral analysis. Do not expect to see good quality of image (it is probably taken from somewhere of the web, but not straight from the EAC), you most likely could not anything in it. Do not stress out. The most important thing is to check for frequency range. All lossy files will have image with cutoff of the frequency below 20 000 (18 000, etc). Lossless wav file (CD quality) has frequencies upto 22 500 Hz.

Look at the image: the white line shows the limit for 20 000 Hz, but the image lossless file shows frequencies above this line!

http://image.torrent-invites.com/images/391spectral.png

To learn more about the subject, here are couple decent links. The first link is what What.CD would recommend for you to look if you fail:

Spectral Comparisons
MP3 vs AAC vs FLAC vs CD | Stereophile.com

More to come.

great stuff mate :D

should we do this in their irc channel ?

This is really great. Thank you!

Originally Posted by BBOSS

great stuff mate :D

should we do this in their irc channel ?

Everything is being done on their irc channel. Here is the link with all necessary info:

What.CD: A Beginner's Guide

­Here are some more real situation questions that just arrived.

Basic audio knowledge.­ You have 10 minutes to answer all questions:

1. What is the difference between lossless and lossy audio codecs? Give two examples for each.
2. What is LAME?
3. What is a transcode?
4. What do VBR and ABR stand for? Explain in as much detail as possible how they work, in the context of LAME and which will achieve the better quality when using the same "target bitrate".
5. Are the following formats lossy or lossless? Are they allowed on What.CD?
a) APE
b) V0
c) WAV (PCM)
d) 128 CBR
e) q8.x Ogg Vorbis
f) SHN
g) 256 VBR
h) V2
i) FLAC
6. What are V0 and V2? What are their target bitrates?
7. What is the main difference between WAV (PCM) and FLAC?


I hope more will come.

I got into What.cd when I had been interviewed for like three hours. Even though I already had all the theory (already got it in my bachelor's/master's education), there was one thing I wished I had studied more (because I found it stressful during the interview when I had a strict time limit to present the answers), and that was the different formats that are allowed on What.cd, i.e. FLAC, MP3-320, AAC-320, MP3-V0, MP3-V2 and Vorbis-q8 and how to rank them, i.e. what is the better quality, MP3-V0 or Vorbis-q8?

Originally Posted by Malevich

I got into What.cd when I had been interviewed for like three hours...
...I had a strict time limit to present the answers), and that was the different formats that are allowed on What.cd, i.e.
FLAC, MP3-320, AAC-320, MP3-V0, MP3-V2 and Vorbis-q8 and how to rank them, i.e. what is the better quality, MP3-V0 or Vorbis-q8?

First of all congratulations! I am glad to hear about your success!

Actually, all these formats have been mentioned in my tutorial. Please look more closely.

I know, the info will be useful for all.

thats very nice tips buddy
will help me a lot with my interview

Originally Posted by YourHero

thats very nice tips buddy
will help me a lot with my interview

Just post something about your experience after you try to pass, will you? Even not passing gives alot of tips! And extra tips will definitely help others.


I have noticed that someone may still be confused when receiving questions about Vorbis.

Here is shortly what you may look for. Vorbis is compression format with general audio compression at bitrates ~64–400 kbps.

Transparency is generally reached at about 150–170 kbps (-q 5).

If you are asked to compare qualities – rely essentially on comparing bit rates of different formats. And the bit rates for Vorbis are below:

Quality = Nominal Bitrate:
-q(-2) --> not available
-q(-1) --> 45 kbit/s
-q0 --> 64 kbit/s
-q1 --> 80 kbit/s
-q2 --> 96 kbit/s
-q3 --> 112 kbit/s
-q4 --> 128 kbit/s
-q5 --> 160 kbit/s
-q6 --> 192 kbit/s
-q7 --> 224 kbit/s
-q8 --> 256 kbit/s
-q9 --> 320 kbit/s
-q10 --> 500 kbit/s


Technical note: (Ogg) Vorbis = Ogg in brackets because Vorbis is commonly used inside Ogg container.

My personal note about the matter: Who cares about some Vorbis or mp3 or whatever lossy format if you are dealing with lossless format only. STOP! This is not what What.CD thinks